github.com/olljanat/moby@v1.13.1/docs/extend/plugin_api.md (about)

     1  ---
     2  title: "Plugins API"
     3  description: "How to write Docker plugins extensions "
     4  keywords: "API, Usage, plugins, documentation, developer"
     5  ---
     6  
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    15  
    16  # Docker Plugin API
    17  
    18  Docker plugins are out-of-process extensions which add capabilities to the
    19  Docker Engine.
    20  
    21  This document describes the Docker Engine plugin API. To view information on
    22  plugins managed by Docker Engine, refer to [Docker Engine plugin system](index.md).
    23  
    24  This page is intended for people who want to develop their own Docker plugin.
    25  If you just want to learn about or use Docker plugins, look
    26  [here](legacy_plugins.md).
    27  
    28  ## What plugins are
    29  
    30  A plugin is a process running on the same or a different host as the docker daemon,
    31  which registers itself by placing a file on the same docker host in one of the plugin
    32  directories described in [Plugin discovery](#plugin-discovery).
    33  
    34  Plugins have human-readable names, which are short, lowercase strings. For
    35  example, `flocker` or `weave`.
    36  
    37  Plugins can run inside or outside containers. Currently running them outside
    38  containers is recommended.
    39  
    40  ## Plugin discovery
    41  
    42  Docker discovers plugins by looking for them in the plugin directory whenever a
    43  user or container tries to use one by name.
    44  
    45  There are three types of files which can be put in the plugin directory.
    46  
    47  * `.sock` files are UNIX domain sockets.
    48  * `.spec` files are text files containing a URL, such as `unix:///other.sock` or `tcp://localhost:8080`.
    49  * `.json` files are text files containing a full json specification for the plugin.
    50  
    51  Plugins with UNIX domain socket files must run on the same docker host, whereas
    52  plugins with spec or json files can run on a different host if a remote URL is specified.
    53  
    54  UNIX domain socket files must be located under `/run/docker/plugins`, whereas
    55  spec files can be located either under `/etc/docker/plugins` or `/usr/lib/docker/plugins`.
    56  
    57  The name of the file (excluding the extension) determines the plugin name.
    58  
    59  For example, the `flocker` plugin might create a UNIX socket at
    60  `/run/docker/plugins/flocker.sock`.
    61  
    62  You can define each plugin into a separated subdirectory if you want to isolate definitions from each other.
    63  For example, you can create the `flocker` socket under `/run/docker/plugins/flocker/flocker.sock` and only
    64  mount `/run/docker/plugins/flocker` inside the `flocker` container.
    65  
    66  Docker always searches for unix sockets in `/run/docker/plugins` first. It checks for spec or json files under
    67  `/etc/docker/plugins` and `/usr/lib/docker/plugins` if the socket doesn't exist. The directory scan stops as
    68  soon as it finds the first plugin definition with the given name.
    69  
    70  ### JSON specification
    71  
    72  This is the JSON format for a plugin:
    73  
    74  ```json
    75  {
    76    "Name": "plugin-example",
    77    "Addr": "https://example.com/docker/plugin",
    78    "TLSConfig": {
    79      "InsecureSkipVerify": false,
    80      "CAFile": "/usr/shared/docker/certs/example-ca.pem",
    81      "CertFile": "/usr/shared/docker/certs/example-cert.pem",
    82      "KeyFile": "/usr/shared/docker/certs/example-key.pem"
    83    }
    84  }
    85  ```
    86  
    87  The `TLSConfig` field is optional and TLS will only be verified if this configuration is present.
    88  
    89  ## Plugin lifecycle
    90  
    91  Plugins should be started before Docker, and stopped after Docker.  For
    92  example, when packaging a plugin for a platform which supports `systemd`, you
    93  might use [`systemd` dependencies](
    94  http://www.freedesktop.org/software/systemd/man/systemd.unit.html#Before=) to
    95  manage startup and shutdown order.
    96  
    97  When upgrading a plugin, you should first stop the Docker daemon, upgrade the
    98  plugin, then start Docker again.
    99  
   100  ## Plugin activation
   101  
   102  When a plugin is first referred to -- either by a user referring to it by name
   103  (e.g.  `docker run --volume-driver=foo`) or a container already configured to
   104  use a plugin being started -- Docker looks for the named plugin in the plugin
   105  directory and activates it with a handshake. See Handshake API below.
   106  
   107  Plugins are *not* activated automatically at Docker daemon startup. Rather,
   108  they are activated only lazily, or on-demand, when they are needed.
   109  
   110  ## Systemd socket activation
   111  
   112  Plugins may also be socket activated by `systemd`. The official [Plugins helpers](https://github.com/docker/go-plugins-helpers)
   113  natively supports socket activation. In order for a plugin to be socket activated it needs
   114  a `service` file and a `socket` file.
   115  
   116  The `service` file (for example `/lib/systemd/system/your-plugin.service`):
   117  
   118  ```
   119  [Unit]
   120  Description=Your plugin
   121  Before=docker.service
   122  After=network.target your-plugin.socket
   123  Requires=your-plugin.socket docker.service
   124  
   125  [Service]
   126  ExecStart=/usr/lib/docker/your-plugin
   127  
   128  [Install]
   129  WantedBy=multi-user.target
   130  ```
   131  The `socket` file (for example `/lib/systemd/system/your-plugin.socket`):
   132  
   133  ```
   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  {
   172      "Implements": ["VolumeDriver"]
   173  }
   174  ```
   175  
   176  Responds with a list of Docker subsystems which this plugin implements.
   177  After activation, the plugin will then be sent events from this subsystem.
   178  
   179  Possible values are:
   180  
   181  * [`authz`](plugins_authorization.md)
   182  * [`NetworkDriver`](plugins_network.md)
   183  * [`VolumeDriver`](plugins_volume.md)
   184  
   185  
   186  ## Plugin retries
   187  
   188  Attempts to call a method on a plugin are retried with an exponential backoff
   189  for up to 30 seconds. This may help when packaging plugins as containers, since
   190  it gives plugin containers a chance to start up before failing any user
   191  containers which depend on them.
   192  
   193  ## Plugins helpers
   194  
   195  To ease plugins development, we're providing an `sdk` for each kind of plugins
   196  currently supported by Docker at [docker/go-plugins-helpers](https://github.com/docker/go-plugins-helpers).