github.com/kaisenlinux/docker.io@v0.0.0-20230510090727-ea55db55fac7/cli/docs/extend/plugin_api.md (about)

     1  ---
     2  description: "How to write Docker plugins extensions "
     3  keywords: "API, Usage, plugins, documentation, developer"
     4  ---
     5  
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    14  
    15  # Docker Plugin API
    16  
    17  Docker plugins are out-of-process extensions which add capabilities to the
    18  Docker Engine.
    19  
    20  This document describes the Docker Engine plugin API. To view information on
    21  plugins managed by Docker Engine, refer to [Docker Engine plugin system](index.md).
    22  
    23  This page is intended for people who want to develop their own Docker plugin.
    24  If you just want to learn about or use Docker plugins, look
    25  [here](legacy_plugins.md).
    26  
    27  ## What plugins are
    28  
    29  A plugin is a process running on the same or a different host as the docker daemon,
    30  which registers itself by placing a file on the same docker host in one of the plugin
    31  directories described in [Plugin discovery](#plugin-discovery).
    32  
    33  Plugins have human-readable names, which are short, lowercase strings. For
    34  example, `flocker` or `weave`.
    35  
    36  Plugins can run inside or outside containers. Currently running them outside
    37  containers is recommended.
    38  
    39  ## Plugin discovery
    40  
    41  Docker discovers plugins by looking for them in the plugin directory whenever a
    42  user or container tries to use one by name.
    43  
    44  There are three types of files which can be put in the plugin directory.
    45  
    46  * `.sock` files are UNIX domain sockets.
    47  * `.spec` files are text files containing a URL, such as `unix:///other.sock` or `tcp://localhost:8080`.
    48  * `.json` files are text files containing a full json specification for the plugin.
    49  
    50  Plugins with UNIX domain socket files must run on the same docker host, whereas
    51  plugins with spec or json files can run on a different host if a remote URL is specified.
    52  
    53  UNIX domain socket files must be located under `/run/docker/plugins`, whereas
    54  spec files can be located either under `/etc/docker/plugins` or `/usr/lib/docker/plugins`.
    55  
    56  The name of the file (excluding the extension) determines the plugin name.
    57  
    58  For example, the `flocker` plugin might create a UNIX socket at
    59  `/run/docker/plugins/flocker.sock`.
    60  
    61  You can define each plugin into a separated subdirectory if you want to isolate definitions from each other.
    62  For example, you can create the `flocker` socket under `/run/docker/plugins/flocker/flocker.sock` and only
    63  mount `/run/docker/plugins/flocker` inside the `flocker` container.
    64  
    65  Docker always searches for unix sockets in `/run/docker/plugins` first. It checks for spec or json files under
    66  `/etc/docker/plugins` and `/usr/lib/docker/plugins` if the socket doesn't exist. The directory scan stops as
    67  soon as it finds the first plugin definition with the given name.
    68  
    69  ### JSON specification
    70  
    71  This is the JSON format for a plugin:
    72  
    73  ```json
    74  {
    75    "Name": "plugin-example",
    76    "Addr": "https://example.com/docker/plugin",
    77    "TLSConfig": {
    78      "InsecureSkipVerify": false,
    79      "CAFile": "/usr/shared/docker/certs/example-ca.pem",
    80      "CertFile": "/usr/shared/docker/certs/example-cert.pem",
    81      "KeyFile": "/usr/shared/docker/certs/example-key.pem"
    82    }
    83  }
    84  ```
    85  
    86  The `TLSConfig` field is optional and TLS will only be verified if this configuration is present.
    87  
    88  ## Plugin lifecycle
    89  
    90  Plugins should be started before Docker, and stopped after Docker.  For
    91  example, when packaging a plugin for a platform which supports `systemd`, you
    92  might use [`systemd` dependencies](
    93  https://www.freedesktop.org/software/systemd/man/systemd.unit.html#Before=) to
    94  manage startup and shutdown order.
    95  
    96  When upgrading a plugin, you should first stop the Docker daemon, upgrade the
    97  plugin, then start Docker again.
    98  
    99  ## Plugin activation
   100  
   101  When a plugin is first referred to -- either by a user referring to it by name
   102  (e.g.  `docker run --volume-driver=foo`) or a container already configured to
   103  use a plugin being started -- Docker looks for the named plugin in the plugin
   104  directory and activates it with a handshake. See Handshake API below.
   105  
   106  Plugins are *not* activated automatically at Docker daemon startup. Rather,
   107  they are activated only lazily, or on-demand, when they are needed.
   108  
   109  ## Systemd socket activation
   110  
   111  Plugins may also be socket activated by `systemd`. The official [Plugins helpers](https://github.com/docker/go-plugins-helpers)
   112  natively supports socket activation. In order for a plugin to be socket activated it needs
   113  a `service` file and a `socket` file.
   114  
   115  The `service` file (for example `/lib/systemd/system/your-plugin.service`):
   116  
   117  ```systemd
   118  [Unit]
   119  Description=Your plugin
   120  Before=docker.service
   121  After=network.target your-plugin.socket
   122  Requires=your-plugin.socket docker.service
   123  
   124  [Service]
   125  ExecStart=/usr/lib/docker/your-plugin
   126  
   127  [Install]
   128  WantedBy=multi-user.target
   129  ```
   130  
   131  The `socket` file (for example `/lib/systemd/system/your-plugin.socket`):
   132  
   133  ```systemd
   134  [Unit]
   135  Description=Your plugin
   136  
   137  [Socket]
   138  ListenStream=/run/docker/plugins/your-plugin.sock
   139  
   140  [Install]
   141  WantedBy=sockets.target
   142  ```
   143  
   144  This will allow plugins to be actually started when the Docker daemon connects to
   145  the sockets they're listening on (for instance the first time the daemon uses them
   146  or if one of the plugin goes down accidentally).
   147  
   148  ## API design
   149  
   150  The Plugin API is RPC-style JSON over HTTP, much like webhooks.
   151  
   152  Requests flow *from* the Docker daemon *to* the plugin.  So the plugin needs to
   153  implement an HTTP server and bind this to the UNIX socket mentioned in the
   154  "plugin discovery" section.
   155  
   156  All requests are HTTP `POST` requests.
   157  
   158  The API is versioned via an Accept header, which currently is always set to
   159  `application/vnd.docker.plugins.v1+json`.
   160  
   161  ## Handshake API
   162  
   163  Plugins are activated via the following "handshake" API call.
   164  
   165  ### /Plugin.Activate
   166  
   167  **Request:** empty body
   168  
   169  **Response:**
   170  
   171  ```json
   172  {
   173      "Implements": ["VolumeDriver"]
   174  }
   175  ```
   176  
   177  Responds with a list of Docker subsystems which this plugin implements.
   178  After activation, the plugin will then be sent events from this subsystem.
   179  
   180  Possible values are:
   181  
   182  * [`authz`](plugins_authorization.md)
   183  * [`NetworkDriver`](plugins_network.md)
   184  * [`VolumeDriver`](plugins_volume.md)
   185  
   186  
   187  ## Plugin retries
   188  
   189  Attempts to call a method on a plugin are retried with an exponential backoff
   190  for up to 30 seconds. This may help when packaging plugins as containers, since
   191  it gives plugin containers a chance to start up before failing any user
   192  containers which depend on them.
   193  
   194  ## Plugins helpers
   195  
   196  To ease plugins development, we're providing an `sdk` for each kind of plugins
   197  currently supported by Docker at [docker/go-plugins-helpers](https://github.com/docker/go-plugins-helpers).