518 lines
24 KiB
ReStructuredText
518 lines
24 KiB
ReStructuredText
=============================
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Octavia v0.5 Component Design
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=============================
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Please refer to the following diagram of the Octavia v0.5 components:
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.. graphviz:: v0.5-component-design.dot
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This milestone release of Octavia concentrates on making the service delivery
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scalable (though individual listeners are not horizontally scalable at this
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stage), getting API and other interfaces between major components correct,
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without worrying about making the command and control layer scalable.
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Note that this design is not yet "operator grade" but is a good first step to
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achieving operator grade (which will occur with version 1 of Octavia).
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================
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LBaaS Components
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================
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The entities in this section describe components that are part of the Neutron
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LBaaS project, with which Octavia interfaces to deliver load balancing
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services.
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USER API HANDLER
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----------------
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This is the front-end that users (and user GUIs or what have you) talk to to
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manipulate load balancing services.
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**Notes:**
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* All implementation details are hidden from the user in this interface
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* Performs a few simple sanity checks on user-supplied data, but otherwise
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looks to a driver provide more detail around whether what the user is asking
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for is possible on the driver's implementation.
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* Any functionality that the user asks for that their back-end flavor / driver
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doesn't support will be met with an error when the user attempts to configure
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services this way. (There may be multiple kinds of errors: "incomplete
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configuration" would be non-fatal and allow DB objects to be created /
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altered. "incompatible configuration" would be fatal and disallow DB objects
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from being created / associations made.) Examples of this include: UDP
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protocol for a listener on a driver/flavor that uses only haproxy as its
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back-end.
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* Drivers should also be able to return 'out of resources' or 'some other
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error occurred' errors (hopefully with helpful error messages).
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* This interface is stateless, though drivers may keep state information in a
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database. In any case, this interface should be highly scalable.
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* Talks some "intermediate driver interface" with the driver. This takes the
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form of python objects passed directly within the python code to the driver.
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=========================
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LBaaS / Octavia Crossover
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=========================
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The entities in this section are "glue" components which allow Octavia to
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interface with other services in the OpenStack environment. The idea here is
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that we want Octavia to be as loosely-coupled as possible with those services
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with which it must interact in order to keep these interfaces as clean as
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possible.
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Initially, all the components in this section will be entirely under the
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purview of the Octavia project. Over time some of these components might be
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eliminated entirely, or reduced in scope as these third-party services
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evolve and increase in cleanly-consumable functionality.
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DRIVER
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------
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This is the part of the load balancing service that actually interfaces between
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the (sanitized) user and operator configuration and the back-end load balancing
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appliances or other "service providing entity."
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**Notes:**
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* Configuration of the driver is handled via service profile definitions in
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association with the Neutron flavor framework. Specifically, a given flavor
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has service profiles associated with it, and service profiles which
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specify the Octavia driver will include meta-data (in the form of JSON
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configuration) which is used by the driver to define implementation
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specifics (for example, HA configuration and other details).
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* Driver will be loaded by the daemon that does the user API and operator API.
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It is not, in and of itself, its own daemon, though a given vendor's back-end
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may contain its own daemons or other services that the driver interfaces
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with.
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* It is thought that the driver front-end should be stateless in order to make
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it horizontally scalable and to preserves the statelessness of the user and
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operator API handlers. Note that the driver may interface with back-end
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components which need not be stateless.
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* It is also possible for multiple instances of the driver will talk to the
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same amphora at the same time. Emphasis on the idempotency of the update
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algorithms used should help minimize the issues this can potentially cause.
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NETWORK DRIVER
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--------------
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In order to keep Octavia's design more clean as a pure consumer of network
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services, yet still be able to develop Octavia at a time when it is impossible
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to provide the kind of load balancing services we need to provide without
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"going around" the existing Neutron API, we have decided to write a "network
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driver" component which does those dirty back-end configuration commands via
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an API we write, until these can become a standard part of Neutron. This
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component should be as loosely coupled with Octavia as Octavia will be with
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Neutron and present a standard interface to Octavia for accomplishing network
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configuration tasks (some of which will simply be a direct correlation with
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existing Neutron API commands).
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**Notes:**
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* This is a daemon or "unofficial extension", presumably living on a Neutron
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network node which should have "back door" access to all things Neutron and
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exposes an API that should only be used by Octavia.
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* Exactly what API will be provided by this driver will be defined as we
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continue to build out the reference implementation for Octavia.
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* Obviously, as we discover missing functionality in the Neutron API, we should
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work with the Neutron core devs to get these added to the API in a timely
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fashion: We want the Network driver to be as lightweight as possible.
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==================
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Octavia Components
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==================
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Everything from here down are entities that have to do with the Octavia driver
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and load balancing system. Other vendor drivers are unlikely to have the same
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components and internal structure. It is planned that Octavia will become the
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new reference implementation for LBaaS, though it of course doesn't need to be
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the only one. (In fact, a given operator should be able to use multiple vendors
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with potentially multiple drivers and multiple driver configurations through
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the Neutron Flavor framework.)
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OPERATOR API HANDLER
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--------------------
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This is exactly like the USER API HANDLER in function, except that
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implementation details are exposed to the operator, and certain admin-level
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features are exposed (ex. listing a given tenant's loadbalancers, & etc.)
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It's also anticipated that the Operator API needs will vary enough from
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implementation to implementation that no single Operator API will be sufficient
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for the needs of all vendor implementations. (And operators will definitely
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have implementation-specific concerns.) Also, we anticipate that most vendors
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will already have an operator API or other interface which is controlled and
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configured outsite the purview of OpenStack in general. As such it makes sense
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for Octavia to have its own operator API / interface.
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**Notes:**
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* This interface is stateless. State should be managd by the controller, and
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stored in a highly available database.
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CONTROLLER
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----------
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This is the component providing all the command and control for the
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amphorae. On the front end, it takes its commands and controls from the LBaaS
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driver.
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It should be noted that in later releases of Octavia, the controller functions
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will be split across several components. At this stage we are less concerned
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with how this internal communcation will happen, and are most concerned with
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ensuring communication with amphorae, the amphora LB driver, and the Network
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driver are all made as perfect as possible.
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Among the controller's responsibilities are:
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* Sending configuration and certificate information to an amphora LB
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driver, which in the reference implementation will be generating
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configuration files for haproxy and PEM-formatted user certificates and
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sending these to individual amphorae. Configuration files will be
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generated from jinja templates kept in an template directory specific to
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the haproxy driver.
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* Processing the configuration updates that need to be applied to individual
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amphorae, as sent by the amphora LB driver.
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* Interfacing with network driver to plumb additional interfaces on the
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amphorae as necessary.
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* Monitoring the health of all amphorae (via a driver interface).
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* Receiving and routing certain kinds of notifications originating on the
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amphorae (ex. "member down")
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* This is a stateful service, and should keep its state in a central, highly
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available database of some sort.
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* Respecting colocation / apolocation requirements of loadbalancers as set
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forth by users.
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* Receiving notifications, statistics data and other short, regular messages
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from amphorae and routing them to the appropriate entity.
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* Responding to requests from amphorae for configuration data.
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* Responding to requests from the user API or operator API handler driver for
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data about specific loadbalancers or sub-objects, their status, and
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statistics.
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* Amphora lifecycle management, including interfacing with Nova and Neutron
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to spin up new amphorae as necessary and handle initial configuration and
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network plumbing for their LB network interface, and cleaning this up when an
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amphora is destroyed.
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* Maintaining a pool of spare amphorae (ie. spawning new ones as necessary
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and deleting ones from the pool when we have too much inventory here.)
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* Gracefully spinning down "dirty old amphorae"
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* Loading and calling configured amphora drivers.
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**Notes:**
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* Almost all the intelligence around putting together and validating
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loadbalancer configurations will live here-- the Amphora API is meant to
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be as simple as possible so that minor feature improvements do not
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necessarily entail pushing out new amphorae across an entire installation.
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* The size of the spare amphora pool should be determined by the flavor
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being offered.
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* The controller also handles spinning up amphorae in the case of a true
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active/standby topology (ie. where the spares pool is effectively zero.) It
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should have enough intelligence to communicate to Nova that these amphorae
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should not be on the same physical host in this topology.
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* It also handles spinning up new amphorae when one fails in the above
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topology.
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* Since spinning up a new amphora is a task that can take a long time, the
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controller should spawn a job or child process which handles this highly
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asynchronous request.
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AMPHORA LOAD BALANCER (LB) DRIVER
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---------------------------------
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This is the abstraction layer that the controller talks to for communicating
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with the amphorae. Since we want to keep Octavia flexible enough so that
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certain components (like the amphora) can be replaced by third party
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products if the operator so desires, it's important to keep many of the
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implementation-specific details contained within driver layers. An amphora
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LB driver also gives the operator the ability to have different open-source
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amphorae with potentially different capabilities (accessed via different
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flavors) which can be handy for, for example, field-testing a new amphora
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image.
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The reference implementation for the amphora LB driver will be for the amphora
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described below.
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Responsibilities of the amphora LB driver include:
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* Generating configuration files for haproxy and PEM-formatted user
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certificates and sending these to individual amphorae. Configuration
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files will be generated from jinja templates kept in an template directory
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specific to the haproxy driver.
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* Handling all communication to and from amphorae.
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LB NETWORK
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----------
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This is the subnet that controllers will use to communicate with amphorae.
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This means that controllers must have connectivity (either layer 2 or routed)
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to this subnet in order to function, and visa versa. Since amphorae will be
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communicating on it, this means the network is not part of the "undercloud."
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**Notes:**
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* As certain sensitive data (TLS private keys, for example) will be transmitted
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over this communication infrastructure, all messages carrying a sensitive
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payload should be done via encrypted and authenticated means. Further, we
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recommend that messages to and from amphorae be signed regardless of the
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sensitivity of their content.
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AMPHORAE
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----------
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This is a Nova VM which actually provides the load balancing services as
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configured by the user. Responsibilities of these entities include:
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* Actually accomplishing the load balancing services for user-configured
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loadbalancers using haproxy.
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* Sending regular heartbeats (which should include some status information).
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* Responding to specific requests from the controller for very basic
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loadbalancer or sub-object status data, including statistics.
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* Doing common high workload, low intelligence tasks that we don't want to
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burden the controller with. (ex. Shipping listener logs to a swift data
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store, if configured.)
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* Sending "edge" notifications (ie. status changes) to the controller when
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members go up and down, when listeners go up and down, etc.
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**Notes:**
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* Each amphora will generally need its own dedicated LB network IP address,
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both so that we don't accidentally bind to any IP:port the user wants to use
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for loadbalancing services, and so that an amphora that is not yet in use
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by any loadbalancer service can still communicate on the network and receive
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commands from its controller. Whether this IP address exists on the same
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subnet as the loadbalancer services it hosts is immaterial, so long as
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front-end and back-end interfaces can be plumbed after an amphora is
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launched.
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* Since amphorae speak to controllers in a "trusted" way, it's important to
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ensure that users do not have command-line access to the amphorae. In
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other words, the amphorae should be a black box from the users'
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perspective.
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* Amphorae will be powered using haproxy 1.5 initially. We may decide to use
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other software (especially for TLS termination) later on.
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* The "glue scripts" which communicate with the controller should be as
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lightweight as possible: Intelligence about how to put together an haproxy
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config, for example, should not live on the amphora. Rather, the amphora
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should perform simple syntax checks, start / restart haproxy if the checks
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pass, and report success/failure of the haproxy restart.
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* With few exceptions, most of the API commands the amphora will ever do
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should be safely handled synchronously (ie. nothing should take longer than a
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second or two to complete).
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* Connection logs, and other things anticipated to generate a potential large
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amount of data should be communicated by the amphora directly to which
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ever service is going to consume that data. (for example, if logs are being
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shunted off to swift on a nightly basis, the amphora should handle this
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directly and not go through the controller.)
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INTERNAL HEALTH MONITORS
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------------------------
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There are actually a few of these, all of which need to be driven by some
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daemon(s) which periodically check that heartbeats from monitored entities are
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both current and showing "good" status, if applicable. Specifically:
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* Controllers need to be able to monitor the availability and overall health
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of amphorae they control. For active amphorae, this check should
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happen pretty quickly: About once every 5 seconds. For spare amphorae,
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the check can happen much more infrequently (say, once per minute).
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The idea here is that internal health monitors will monitor a periodic
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heartbeat coming from the amphorae, and take appropriate action (assuming
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these are down) if they fail to check in with a heartbeat frequently enough.
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This means that internal health monitors need to take the form of a daemon
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which is constantly checking for and processing heartbeat requests (and
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updating controller or amphorae statuses, and triggering other events as
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appropriate).
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======================================================
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Some notes on Controller <-> Amphorae communications
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======================================================
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In order to keep things as scalable as possible, the thought was that short,
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periodic and arguably less vital messages being emitted by the amphora and
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associated controller would be done via HMAC-signed UDP, and more vital, more
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sensitive, and potentially longer transactional messages would be handled via a
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RESTful API on the controller, accessed via bi-directionally authenticated
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HTTPS.
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Specifically, we should expect the following to happen over UDP:
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* heartbeats from the amphora VM to the controller
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* stats data from the amphora to the controller
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* "edge" alert notifications (change in status) from the amphora to the
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controller
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* Notification of pending tasks in queue from controller to amphora
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And the following would happen over TCP:
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* haproxy / tls certificate configuration changes
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=================================================
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Supported Amphora Virtual Appliance Topologies
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=================================================
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Initially, I propose we support two topologies with version 0.5 of Octavia:
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Option 1: "Single active node + spares pool"
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--------------------------------------------
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* This is similar to what HP is doing right now with Libra: Each amphora is
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stand-alone with a frequent health-check monitor in place and upon failure,
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an already-spun-up amphora is moved from the spares pool and configured to
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take the old one's place. This allows for acceptable recovery times on
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amphora failure while still remaining efficient, as far as VM resource
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utilization is concerned.
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Option 2: "True Active / Standby"
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---------------------------------
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* This is similar to what Blue Box is doing right now where amphorae are
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deployed in pairs and use corosync / pacemaker to monitor each other's health
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and automatically take over (usually in less than 5 seconds) if the "active"
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node fails. This provides for the fastest possible recovery time on hardware
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failure, but is much less efficient, as far as VM resource utilization is
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concerned.
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* In this topology a floating IP address (different from a Neutron floating
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IP!) is used to determine which amphora is the "active" one at any given
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time.
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* In this topology, both amphorae need to be colocated on the same subnet.
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As such a "spares pool" doesn't make sense for this type of layout, unless
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all spares are on the same mamangement network with the active nodes.
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We considered also supporting "Single node" topology, but this turns out to be
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the same thing as option 1 above with a spares pool size of zero.
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============================
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Supported Network Topologies
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============================
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This is actually where things get tricky, as far as amphora plumbing is
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concerned. And it only grows trickier when we consider that front-end
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connectivity (ie. to the 'loadbalancer' vip_address) and back-end connectivity
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(ie. to members of a loadbalancing pool) can be handled in different ways.
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Having said this, we can break things down into LB network, front-end and
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back-end topology to discuss the various possible permutations here.
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LB Network
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----------
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Each amphora needs to have a connection to a LB network. And each controller
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needs to have access to this management network (this could be layer-2 or
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routed connectivity). Command and control will happen via the amphorae's
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LB network IP.
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Front-end topologies
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--------------------
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There are generally two ways to handle the amphorae's connection to the
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front-end IP address (this is the vip_address of the loadbalancer object):
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**Option 1: Layer-2 connectivity**
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The amphora can have layer-2 connectivity to the neutron network which is
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host to the subnet on which the loadbalancer vip_address resides. In this
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scenario, the amphora would need to send ARP responses to requests for the
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vip_address, and therefore amphorae need to have interfaces plumbed on said
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vip_address subnets which participate in ARP.
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Note that this is somewhat problematic for active / standby virtual appliance
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topologies because the vip_address for a given load balancer effectively
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becomes a highly-available IP address (a true floating VIP), which means on
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service failover from active to standby, the active amphora needs to
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relenquish all the vip_addresses it has, and the standby needs to take them
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over *and* start up haproxy services. This is OK if a given amphora
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only has a few load balancers, but can lead to several minutes' down-time
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during a graceful failover if there are a dozen or more load balancers on the
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active/standby amphora pair. It's also more risky: The standby node might
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not be able to start up all the haproxy services during such a
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failover. What's more, most types of VRRP-like services which handle floating
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IPs require amphorae to have an additional IP address on the subnet housing
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the floating vip_address in order for the standby amphora to monitor the
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active amphora.
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Also note that in this topology, amphorae need an additional virtual network
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interface plumbed when new front-end loadbalancer vip_addresses are assigned to
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them which exist on subnets to which they don't already have access.
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**Option 2: Routed (layer-3) connectivity**
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In this layout, static routes are injected into the routing infrastructure
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(Neutron) which essentially allow traffic destined for any given loadbalancer
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vip_address to be routed to an IP address which lives on the amphora. (I
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would recommend this be something other than the LB network IP.) In this
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topology, it's actually important that the loadbalancer vip_address does *not*
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exist in any subnet with potential front-end clients because in order for
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traffic to reach the loadbalancer, it must pass through the routing
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infrastructure (and in this case, front-end clients would attempt layer-2
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connectivity to the vip_address).
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This topology also works much better for active/standby configurations, because
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both the active and standby amphorae can bind to the vip_addresses of all
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their assigned loadbalancer objects on a dummy, non-ARPing interface, both can
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be running all haproxy services at the same time, and keep the
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standby server processes from interfering with active loadbalancer traffic
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through the use of fencing scripts on the amphorae. Static routing is
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accomplished to a highly available floating "routing IP" (using some VRRP-like
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service for just this IP) which becomes the trigger for the fencing scripts on
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the amphora. In this scenario, fail-overs are both much more reliable, and
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can be accomplished in usually < 5 seconds.
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Further, in this topology, amphorae do not need any additional virtual
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interfaces plumbed when new front-end loadbalancer vip_addresses are assigned
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to them.
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Back-end topologies
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-------------------
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There are also two ways that amphorae can potentially talk to back-end
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member IP addresses. Unlike the front-end topologies (where option 1 and option
|
|
2 are basically mutually exclusive, if not practically exclusive) both of these
|
|
types of connectivity can be used on a single amphora, and indeed, within a
|
|
single loadbalancer configuration.
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|
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**Option 1: Layer-2 connectivity**
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This is layer-2 connectivity to back-end members, and is implied when a member
|
|
object has a subnet_id assigned to it. In this case, the existence of the
|
|
subnet_id implies amphorae need to have layer-2 connectivity to that subnet,
|
|
which means they need to have a virtual interface plumbed to it, as well as an
|
|
IP address on the subnet. This type of connectivity is useful for "secure"
|
|
back-end subnets that exist behind a NATing firewall where PAT is not in use on
|
|
the firewall. (In this way it effectively bypasses the firewall.) We anticipate
|
|
this will be the most common form of back-end connectivity in use by most
|
|
OpenStack users.
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**Option 2: Routed (layer-3) connectivity**
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|
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|
This is routed connectivity to back-end members. This is implied when a member
|
|
object does not have a subnet_id specified. In this topology, it is assumed
|
|
that member ip_addresses are reachable through standard neutron routing, and
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|
therefore connections to them can be initiated from the amphora's default
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|
gateway. No new virtual interfaces need to be plumbed for this type of
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|
connectivity to members.
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