k8s-docker-suite-app-murano/DockerInterfacesLibrary

Docker Interface Library

This library provides 3 major things:

• DockerApplication: base class that all Docker applications must inherit. Provides a way to define image name and docker container parameters.
• DockerContainerHost: interface for applications that provide Docker application hosting capabilities. Docker applications use this interface to deploy themselves on the Docker host.
• Data structures that are pass between DockerApplications and DockerContainerHosts. They define things like volumes, ports etc. Most important data structure is DockerContainer which describes the container itself.

DockerApplication

This is the base class for all Docker applications. At minimum all inheritors must provide an implementation of getContainer method. Everything else is either optional or implemented in the base class.

It has the following properties:

• `host`: an instance of DockerContainerHost. This is the hosting provider (DockerStandaloneHost, KubernetesPod, etc.) that applications should be deployed to.
• `applicationEndpoints`: output property that is filled with application endpoints after deployment. See below for exact format details.

Class also has the following methods:

• `getContainer`: returns an instance of DockerContainer class that describes container information. Alternatively method can return a properties dictionary that would automatically be converted to DockerContainer by MuranoPL. This method must be implemented by inheritors!

• `deploy`: used to deploy Docker application on given DockerContainerHost. This method is already implemented in this class and should not be overridden by inheritors. It relies on the information returned by getContainer.

• `getConnectionTo`: used to get full endpoint for another Docker application's port when there is a need to connect two Docker applications. Requires three parameters:

  • `application`: an instance of DockerApplication that we want to talk to.
  • `port`: port number of the target application.
  • `protocol`: TCP or UDP.

  Returns a dictionary with two keys - host and port that represent the endpoint. Note that target application must be deployed before calling this method so it is advised to call deploy() first.

  See DockerGrafana/DockerInfluxDB as an example or connected Docker applications.

• `onInstallationStart`: a method that get get called when installation starts. May be overridden by inheritor class to provide extra logging or reporting.

• `onInstallationFinish`: a method that get get called when installation ends. May be overridden by inheritor class to provide extra logging or reporting.

DockerContainer

This is a data structure defining a Docker container.

It has the following properties:

• `name`: container name. Must be unique within single DockerContainerHost. This is the same as application name for regular applications.
• `image`: Docker image name.
• `commands`: optional list of shell commands to execute upon container start.
• `env`: a dictionary of environment key-values (inputs for Docker containers)
• `ports`: a list of ApplicationPort instances. This is a list of ports that need to be opened/exposed by the container.
• `volumes`: an optional mapping that defines volumes that need to be mounted into Docker container. Keys are the paths within container and values are instances of DockerVolume.
• `privileged`: a flag that forces running container in privileged mode.

ApplicationPort

Defines a network port that need to be exposed by the application. This is a structure with three properties:

• `port`: port number
• `protocol`: TCP or UDP
• `scope`: one of public, cloud, host or internal. This property specifies the scope of port visibility: within the single docker instance (on single server) - host, within single DockerContainerHost - internal, single OpenStack cloud - cloud or public for ports that are bind to public floating IP.

DockerVolume

Represents base class for Docker volumes. One of the two inheritors must be used:

• `DockerTempVolume`: temporary storage space
• `DockerHostVolume`: a directory on the host machine that is mounted inside container. The path on host server is specified by the path property of DockerHostVolume.

DockerContainerHost

Defines an interface that all applications capable of hosting Docker applications must implement. Currently there are two implementations of this interface: DockerStandaloneHost and KubernetesPod.

It has the following property:

• `name`: name of the application instance.

It also has the following methods:

• `hostContainer`: Docker applications call this method to register Docker containers on the Docker host during deployment. It accepts single argument -container - an instance of DockerContainer class.

  `deleteContainer`: deletes container from Docker host. Container is identified by its name through name parameter.

  `getEndpoints`: returns a list of endpoints for specified Docker container Container is identified by its name through applicationName parameter. See below on endpoint format specification.

  `getInternalScopeId`: returns an common identifier for all Docker hosts belonging to the same container manager (host aggregation used to group together endpoints of internal scope.

Endpoint representation

Docker container hosts are responsible for management of application endpoints. Application define what ports they want to expose and what should be the scope of visibility for those ports. It is up to the host to map those ports to ports on hosting server and OpenStack floating IPs.

Single port on the container might be accesses in different ways. It usually it may be accessed using 127.0.0.1 address from other containers on the same server, using internal IP from containers on the same cluster, using internal OpenStack server IP from other servers in the same environment or using floating IP for external access. Scope defines maximum level of visibility in the order host -> internal -> cloud -> public. Each subsequent scope extends the visibility for the previous one. So if the application wants a public endpoint for its port the host allocates four endpoints for that port starting from 127.0.0.1:port to access it from the same server and up to FIP:port to access it from the Internet. Thus each port/protocol pair results in 1-4 entries in applicationEndpoints list.

Each entry of that list is a dictionary that has the following keys:

• `address`: IP or hostname.
• `port`: port number that caller must use to access the application.
• `scope`: greatest visibility scope name for the endpoint.
• `portScope`: scope name for the port endpoint was allocated for. For example if ApplicationPort had a 'local` scope then two endpoints will be allocated (host and local and each of them will have local in portScope).
• `containerPort`: port number inside the container.
• `protocol`: TCP or UDP. There can be two endpoints with the same port number that differ only in protocol.

Tips on Docker applications development

• MuranoPL can automatically convert dictionaries to an instances of appropriate class when passing it as an input to a function that has proper class() contract on that value. Thus in most cases data structures can be represented as a dictionaries of property name->value form rather than as MuranoPL objects (thus no need to use new() function to construct them)
• Use getConnectionTo method of DockerApplication to get endpoint to access one docker application from another. If application A wants to talk to application B then this method is called on A with an information about what port of B it requires. The method is smart enough to return the nearest endpoint. This if both A and B are located on the same server returned endpoint will likely to have 127.0.0.1 as an address.
• Call deploy() on dependent applications before retrieving endpoints or obtaining connections to it.