353 lines
14 KiB
ReStructuredText
353 lines
14 KiB
ReStructuredText
===================================
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Deploy Kolla images with Kubernetes
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===================================
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https://blueprints.launchpad.net/kolla/+spec/kolla-kubernetes
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Kubernetes was evaluated by the Kolla team in the first two months of the
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project and it was found to be problematic because it did not support net=host,
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pid=host, and --privileged features in docker. Since then, it has developed
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these features [1].
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The objective is to manage the lifecycle of containerized OpenStack services by
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using Kubernetes container managment tools in order to obtain the self-healing
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and upgrade capabilities inherent in Kubernetes.
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Problem description
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===================
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Kubernetes
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- life-cycle management: service monitoring, HA, loadbalancing, and
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health checks
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- upgrades: rolling
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Kubernetes has services that provide kolla-kubernetes with service monitoring,
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health checks, service scaling, and upgrades. The community can use the
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scheduler and node affinity trait to assign work loads to appropriate nodes [2].
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Kubernetes also has built in health checks that monitors a container's status.
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Finally, kolla-kubernetes can use the replication controller to scale up and
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down the stack [3].
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For upgrades, Kubernetes has an object called 'deployments'[4], which detects
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when a pod needs to change. It starts to scale down the current running
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pods and scale up the new pods.
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Use Cases
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=========
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- Kubernetes as an underlay for OpenStack.
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- Kubernetes to handle container scheduling.
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- Feedback loop when using Kubernetes health checks during deployment and
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upgrade.
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- High Availability for individual containers
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Proposed change
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===============
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- Add a deployment specific git repo (kolla-kubernetes) under the kolla
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governance that contains the Kubernetes deployment code.
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Orchestration
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-------------
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OpenStack on Kubernetes will be orchestrated by outside tools in order to create
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a production ready OpenStack environment. The kolla-kubernetes repo is where
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any deployment tool can join the community and be a part of orchestrating a
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kolla-kubernetes deployment.
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Service Config Management
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-------------------------
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Config generation will be completely decoupled from the deployment. The
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containers only expect a config file to land in a specific directory in
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the container in order to run. With this decoupled model, any tool could be
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used to generate config files. The kolla-kubernetes community will evaluate
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any config generation tool, but will likely use Ansible for config generation
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in order to reuse existing work from the community. This solution uses
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customized Ansible and jinja2 templates to generate the config. Also, there will
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be a maintained set of defaults and a global yaml file that can override the
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defaults.
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The config files will be injected into the kubernetes configmap and loaded into
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the containers. There will be one configmap per configuration file and there can
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be multiple config maps. The containers will configure themselves using the
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configuration files loaded into the appropriate directories [5][6].
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Bootstrapping
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-------------
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Bootstrapping the Kolla containers involves running a single task per service
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that will initialize the databases and create the users. The bootstrapping task
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will be a Kubernetes Job, which will run the task until completion then
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terminate the pods [7].
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Each service will have a bootstrap task so that when the operator upgrades,
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the bootstrap tasks are reused to upgrade the database. This will allow
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deployment and upgrades to follow the same pipeline.
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The Kolla containers will communicate with the Kubernetes API server to in order
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to be self aware of if any bootstrapping processes are occuring.
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Alternative bootstrap approaches:
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1) Create 2 pods per OpenStack service. One pod is designed to do the
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bootstrapping/db_sync while the other pod runs as the normal service. This will
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require some orchestration and the bootstrap pod will need to be setup to
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never restart or be replicated.
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2) Use a sidecar container in the pod to handle the database sync with proper
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health checking to make sure the services are coming up healthy. The big
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difference between kolla's old docker-compose solution and Kubernetes, is that
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docker-compose would only restart the containers. Kubernetes will completely
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reschedule them. Which means, removing the pod and restarting it. The reason
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this would fix that race condition failure kolla saw from docker-compose is
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because glance would be rescheduled on failure allowing keystone to get a
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chance to sync with the database and become active instead of constantly being
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piled with glance requests. There can also be health checks around this to help
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determine order.
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If kolla-kubernetes used this sidecar approach, it would regain the use of
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native Kubernetes upgrades [16].
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Dependencies
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------------
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- Kubernetes >= 1.3.0
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- Docker >= 1.10.0
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- Jinja2 >= 2.8.0
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Kubernetes does not support dependencies between pods. The operator will launch
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all the services and use kubernetes health checks to bring the deployment to an
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operational state.
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With orchestration around Kubernetes, the operator can determine what tasks are
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run and when the tasks are run. This way, dependencies are handled at the
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orchestration level, but they are not required because proper health checking
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will bring up the cluster in a healthy state.
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Upgrades
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--------
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Kubernetes has an object called a Deployment, where the operator defines a
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desired state for the pods and the deployment will move the cluster to the
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desired state when a change is detected.
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Kolla-kubernetes will provide Jobs that will provide the operator with the
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flexibility needed to under go a step wise upgrade. In future releases,
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kolla-kubernetes will look to Kubernetes to provide a means for operators to
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plugin these jobs into a Deployment.
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Reconfigure
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-----------
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The operator generates a new config and loads it into the Kubernetes configmap
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by changing the configmap version in the service yaml file. Then, the operator
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will trigger a rolling upgrade, which will scale down old pods and bring up new
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ones that will run with the updated configuration files.
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There's an open issue upstream in Kubernetes where the plan is to add support
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around detecting if a pod has a changed in the configmap [6]. Depending on what
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the solution is, kolla-kubernetes may or may not use it. The rolling
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upgrade feature will provide kolla-kubernetes with an elegant way to handle
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restarting the services.
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HA Architecture
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---------------
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Kubernetes uses health checks to bring up the services. Therefore,
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kolla-kubernetes will use the same checks when monitoring if a service is
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healthy. When a service fails, the replication controller will be responsible
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for bringing up a new container in its place [8][9].
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However, Kubernetes does not cover all the HA corner cases, for instance,
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fencing. But, there are some operator known practices that can be used to get
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around this [10]. For example, to implement storage fencing, the operator can
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use ceph backed storage [11][12]. This is an option that the community can
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document in order to provide kolla-kubernetes with a production ready solution
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if Kubernetes cannot.
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.. note:: There is a known issue in Kubernetes with releasing volumes from a
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node that disappeared from the cluster. This is expected to be fixed in the 1.3
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release [13].
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Persistent Storage
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------------------
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Kubernetes has many types of persistent storage [14]. Since Kubernetes doesn't
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guarantee a pod will always be scheduled to a host, it makes node based
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persistent storage unlikely, unless the community uses labels for every pod.
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Persistent storage in kolla-kubernetes will come from volumes backed by
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different storage offerings to provide persistent storage. Kolla-kubernetes
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will provide a default solution using Ceph RBD, that the community will use to
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deploy multinode with. From there, kolla-kubernetes can add any additional
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persistent storage options as well as support options for the operator to
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reference an existing storage solution.
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To deploy Ceph, the community will use the Ansible playbooks from Kolla to
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deploy a containerized Ceph at least for the 1.0 release. After Kubernetes
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deployment matures, the community can evaluate building its own Ceph deployment
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solution.
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Existing external Ceph deployments will require additional documentation
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to describe how to integrate them with a Kubernetes deployment.
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Service Roles
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-------------
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At the broadest level, OpenStack can split up into two main roles, Controller
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and Compute. With Kubernetes, the role definition layer changes.
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Kolla-kubernetes will still need to define Compute nodes, but not Controller
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nodes. Compute nodes hold the libvirt container and the running vms. That
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service cannont migrate because the vms associated with it exist on the node.
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However, the Controller role is more flexible. The Kubernetes layer provides IP
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persistence so that APIs will remain active and abstracted from the operator's
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view [15]. kolla-kubernetes can direct Controller services away from the Compute
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node using labels, while managing Compute services more strictly.
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The Kubernetes Label field will be configurable to allow the operator to
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define roles and direct where services will land.
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Security impact
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---------------
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Kolla-Kubernetes will run the containers as non root wherever possible.
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SELinux or AppArmor will be in place to limit the damage from container
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breakouts.
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Kubernetes is planning to adding capabilities to the pod level that will enable
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the community to restrict container privileges even further [16].
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Performance Impact
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------------------
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Since kolla-kubernetes is not using dependencies for the service deployment, the
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services will take a different amount of time to start up for each deployment
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because the order will always vary when the services become active.
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As such, it's hard to quantify the exact performance impact other than it is
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small.
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Networking
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----------
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Kolla-kubernetes will initially use 'net=host' everywhere to get the project
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going. As the project matures, 'net=host' needs to be reevaluated as to which
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services will run without 'net=host' in order to gain additional functionality.
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For example, controller services will float between nodes potentially landing
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two of the same pods on the same node. Those pods will be listening on the same
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ports in the hosts network stack, which could prevent the pods from working.
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Logging & Monitoring
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--------------------
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To reuse Kolla's containers, kolla-kubernetes will use elastic search, heka, and
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kibana as the default logging mechanism.
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The community will implement centralized logging by using a 'side car' container
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in the Kubernetes pod [17]. The logging service will trace the logs from the
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shared volume of the running serivce and send the data to elastic search. This
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solution is ideal because volumes are shared amoung the containers in a pod.
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Implementation
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==============
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Primary Assignee(s)
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-----------
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Ryan Hallisey (rhallisey)
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Other contributor(s):
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kolla-core team [18]
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Alex Polvi (polvi)
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Andrew Battye
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Brandon Jozsa (v1k0d3n)
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Britt Houser (britthouser)
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Davanum Srinivas (dims)
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David Wang (dcwangmit01)
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Egor Guz (eghobo)
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Greg Herlein (gherlein)
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Hui Kang (huikang)
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Ian Main (Slower)
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Jinay Vora (jvora)
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Keith Byrne (kbyrne)
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Ken Wronkiewicz (wirehead)
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Kevin Fox (kfox1111)
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Marga Millet (fragatina)
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Marian Schwarz
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Mark Casey (mark-casey)
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Mauricio Lima (mlima)
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Md Nadeem (mail2nadeem92)
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Michael Schmidt
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Michal Rostecki (mrostecki)
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Qiu Yu (unicell)
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Rajath Agasthya (rajathagasthya)
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Rob Mason
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Sean Mooney (sean-k-mooney)
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Serguei Bezverkhi (sbezverk)
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Sidharth Surana (ssurana)
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Zdenek Janda (xdeu)
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<Please add your name here if you are getting involved in kolla-kubernetes>
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Milestones
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----------
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Target Milestone for tech-preview code:
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Newton
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Work Items
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----------
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1. Create kolla-kubernetes repo
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2. Build yaml files for each service
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3. Build a CLI to handle templated yaml files
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4. Build an all in one environment
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5. Drop net=host on a set of services
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6. Write per service health checks
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7. Write startup docs
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8. Add orchestration tools around the pods
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9. All in one gating
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10. Convert each service to a 'Deployment'
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11. Build multinode environment
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12. Config generation tools
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13. Multinode docs
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14. Implement reconfigure by templating configmaps
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15. Centralized logging
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16. Implement upgrades
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17. Advanced deployment docs
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<Please add new work items that are worth mentioning in the spec>
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Testing
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=======
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Functional tests will be implemented in the OpenStack check/gating system to
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automatically test that the Kubernetes deployment works for an AIO
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environment [19].
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Documentation Impact
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====================
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Add a quick start guide, which explains how to deploy kolla-kubernetes.
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Add a developer guide on how to contribute which also explains how the
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deployment works.
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References
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==========
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- [1] https://github.com/kubernetes/kubernetes/releases/tag/v1.2.0
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- [2] http://kubernetes.io/docs/user-guide/node-selection/
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- [3] http://kubernetes.io/v1.0/docs/user-guide/managing-deployments.html
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- [4] https://cloud.google.com/container-engine/docs/replicationcontrollers/
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- [5] https://github.com/kubernetes/kubernetes/blob/master/docs/design/configmap.md
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- [6] https://github.com/kubernetes/kubernetes/issues/24957
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- [7] http://kubernetes.io/docs/user-guide/jobs/
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- [8] http://kubernetes.io/docs/user-guide/replication-controller/
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- [9] http://kubernetes.io/docs/user-guide/replicasets/
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- [10] http://kubernetes.io/docs/admin/high-availability/#master-elected-components
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- [11] http://kubernetes.io/docs/user-guide/volumes/#rbd
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- [12] http://docs.ceph.com/docs/master/cephfs/eviction/
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- [13] https://github.com/kubernetes/kubernetes/issues/20262
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- [14] http://kubernetes.io/docs/user-guide/volumes/
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- [15] http://kubernetes.io/docs/user-guide/node-selection/
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- [16] https://github.com/kubernetes/kubernetes/blob/master/docs/proposals/pod-security-context.md
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- [17] http://blog.kubernetes.io/2015/06/the-distributed-system-toolkit-patterns.html
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- [18] https://review.openstack.org/#/admin/groups/460,members
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- [19] https://etherpad.openstack.org/p/kolla-newton-summit-kolla-gate-walkthru
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- https://github.com/kubernetes/kubernetes
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