Expand on the definition of our ops
Signed-off-by: Doug Davis <dug@us.ibm.com>
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Doug Davis
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runtime.md
130
runtime.md
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# Runtime and Lifecycle
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## Scope of a Container
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Barring access control concerns, the entity using a runtime to create a container MUST be able to use the operations defined in this specification against that same container.
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Whether other entities using the same, or other, instance of the runtime can see that container is out of scope of this specification.
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## State
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Runtime MUST store container metadata on disk so that external tools can consume and act on this information.
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It is recommended that this data be stored in a temporary filesystem so that it can be removed on a system reboot.
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On Linux/Unix based systems the metadata MUST be stored under `/run/opencontainer/containers`.
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For non-Linux/Unix based systems the location of the root metadata directory is currently undefined.
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Within that directory there MUST be one directory for each container created, where the name of the directory MUST be the ID of the container.
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For example: for a Linux container with an ID of `173975398351`, there will be a corresponding directory: `/run/opencontainer/containers/173975398351`.
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Within each container's directory, there MUST be a JSON encoded file called `state.json` that contains the runtime state of the container.
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For example: `/run/opencontainer/containers/173975398351/state.json`.
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The state of a container MUST include, at least, the following propeties:
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The `state.json` file MUST contain all of the following properties:
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* **`version`**: (string) is the OCF specification version used when creating the container.
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* **`ociVersion`**: (string) is the OCI specification version used when creating the container.
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* **`id`**: (string) is the container's ID.
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This MUST be unique across all containers on this host.
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There is no requirement that it be unique across hosts.
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@ -23,37 +19,111 @@ This allows the hooks to perform cleanup and teardown logic after the runtime de
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* **`bundlePath`**: (string) is the absolute path to the container's bundle directory.
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This is provided so that consumers can find the container's configuration and root filesystem on the host.
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*Example*
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When serialized in JSON, the format MUST adhere to the following pattern:
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```json
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{
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"version": "0.2.0",
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"id": "oc-container",
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"ociVersion": "0.2.0",
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"id": "oci-container1",
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"pid": 4422,
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"bundlePath": "/containers/redis"
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}
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```
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See [Query State](#query-state) for information on retrieving the state of a container.
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## Lifecycle
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The lifecycle describes the timeline of events that happen from when a container is created to when it ceases to exist.
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1. OCI compliant runtime is invoked by passing the bundle path as argument.
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2. The container's runtime environment is created according to the configuration in [`config.json`](config.md).
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Any updates to `config.json` after container is running do not affect the container.
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3. The container's state.json file is written to the filesystem.
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4. The prestart hooks are invoked by the runtime.
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If any prestart hook fails, then the container is stopped and the lifecycle continues at step 8.
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5. The user specified process is executed in the container.
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6. The poststart hooks are invoked by the runtime.
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If any poststart hook fails, then the container is stopped and the lifecycle continues at step 8.
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7. Additional actions such as pausing the container, resuming the container or signaling the container may be performed using the runtime interface.
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The container could also error out or crash.
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8. The container is destroyed by undoing the steps performed during create phase (step 2).
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9. The poststop hooks are invoked by the runtime and errors, if any, are logged.
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10. The state.json file associated with the container is removed and the return code of the container's user specified process is returned or logged.
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1. OCI compliant runtime is invoked with a reference to the location of the bundle.
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How this reference is passed to the runtime is an implementation detail.
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2. The container's runtime environment MUST be created according to the configuration in [`config.json`](config.md).
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Any updates to `config.json` after container is running MUST not affect the container.
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3. The prestart hooks MUST be invoked by the runtime.
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If any prestart hook fails, then the container MUST be stopped and the lifecycle continues at step 8.
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4. The user specified process MUST be executed in the container.
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5. The poststart hooks MUST be invoked by the runtime.
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If any poststart hook fails, then the container MUST be stopped and the lifecycle continues at step 8.
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6. Additional actions such as pausing the container, resuming the container or signaling the container MAY be performed using the runtime interface.
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The container MAY also error out, exit or crash.
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7. The container MUST be destroyed by undoing the steps performed during create phase (step 2).
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8. The poststop hooks MUST be invoked by the runtime and errors, if any, MAY be logged.
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Note: The lifecycle is a WIP and it will evolve as we have more use cases and more information on the viability of a separate create phase.
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## Operations
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OCI compliant runtimes MUST support the following operations, unless the operation is not supported by the base operating system.
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### Errors
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In cases where the specified operation generates an error, this specification does not mandate how, or even if, that error is returned or exposed to the user of an implementation.
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Unless otherwise stated, generating an error MUST leave the state of the environment as if the operation were never attempted - modulo any possible trivial ancillary changes such as logging.
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### Query State
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`state <container-id>`
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This operation MUST generate an error if it is not provided the ID of a container.
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This operation MUST return the state of a container as specified in the [State](#state) section.
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In particular, the state MUST be serialized as JSON.
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### Start
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`start <container-id> <path-to-bundle>`
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This operation MUST generate an error if it is not provided a path to the bundle and the container ID to associate with the container.
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If the ID provided is not unique across all containers within the scope of the runtime, or is not valid in any other way, the implementation MUST generate an error.
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Using the data in `config.json`, that are in the bundle's directory, this operation MUST create a new container.
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This includes creating the relevant namespaces, resource limits, etc and configuring the appropriate capabilities for the container.
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A new process within the scope of the container MUST be created as specified by the `config.json` file otherwise an error MUST be generated.
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Attempting to start an already running container MUST have no effect on the container and MUST generate an error.
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### Stop
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`stop <container-id>`
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This operation MUST generate an error if it is not provided the container ID.
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This operation MUST stop and delete a running container.
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Stopping a container MUST stop all of the processes running within the scope of the container.
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Deleting a container MUST delete the associated namespaces and resources associated with the container.
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Once a container is deleted, its `id` MAY be used by subsequent containers.
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Attempting to stop a container that is not running MUST have no effect on the container and MUST generate an error.
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### Exec
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`exec <container-id> <path-to-json>`
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This operation MUST generate an error if it is not provided the container ID and a path to the JSON describing the process to start.
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The JSON describing the new process MUST adhere to the [Process configuration](config.md#process-configuration) definition.
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This operation MUST create a new process within the scope of the container.
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If the container is not running then this operation MUST have no effect on the container and MUST generate an error.
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Executing this operation multiple times MUST result in a new process each time.
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Example:
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```
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{
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"terminal": true,
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"user": {
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"uid": 0,
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"gid": 0,
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"additionalGids": null
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},
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"args": [
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"/bin/sleep",
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"60"
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],
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"env": [
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"version=1.0"
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],
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"cwd": "...",
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}
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```
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This specification does not manadate the name of this JSON file.
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See the specification of the `config.json` file for the definition of these fields.
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The stopping, or exiting, of these secondary process MUST have no effect on the state of the container.
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In other words, a container (and its PID 1 process) MUST NOT be stopped due to the exiting of a secondary process.
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## Hooks
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See [runtime configuration for hooks](./config.md#hooks)
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Many of the operations specified in this specification have "hooks" that allow for additional actions to be taken before or after each operation.
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See [runtime configuration for hooks](./config.md#hooks) for more information.
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