--- layout: "docs" page_title: "Drivers: Docker" sidebar_current: "docs-drivers-docker" description: |- The Docker task driver is used to run Docker based tasks. --- # Docker Driver Name: `docker` The `docker` driver provides a first-class Docker workflow on Nomad. The Docker driver handles downloading containers, mapping ports, and starting, watching, and cleaning up after containers. ## Task Configuration The `docker` driver is configured via a `config` block: ``` task "webservice" { driver = "docker" config = { image = "redis" labels = { group = "webservice-cache" } } } ``` The following options are available for use in the job specification. * `image` - The Docker image to run. The image may include a tag or custom URL and should include `https://` if required. By default it will be fetched from Docker Hub. * `command` - (Optional) The command to run when starting the container. * `args` - (Optional) A list of arguments to the optional `command`. If no `command` is present, `args` are ignored. References to environment variables or any [interpretable Nomad variables](/docs/jobspec/interpreted.html) will be interpreted before launching the task. For example: ``` args = ["${nomad.datacenter}", "${MY_ENV}", "${meta.foo}"] ``` * `labels` - (Optional) A key/value map of labels to set to the containers on start. * `privileged` - (Optional) `true` or `false` (default). Privileged mode gives the container access to devices on the host. Note that this also requires the nomad agent and docker daemon to be configured to allow privileged containers. * `ipc_mode` - (Optional) The IPC mode to be used for the container. The default is `none` for a private IPC namespace. Other values are `host` for sharing the host IPC namespace or the name or id of an existing container. Note that it is not possible to refer to Nomad started Docker containers since their names are not known in advance. Note that setting this option also requires the Nomad agent to be configured to allow privileged containers. * `pid_mode` - (Optional) `host` or not set (default). Set to `host` to share the PID namespace with the host. Note that this also requires the Nomad agent to be configured to allow privileged containers. * `uts_mode` - (Optional) `host` or not set (default). Set to `host` to share the UTS namespace with the host. Note that this also requires the Nomad agent to be configured to allow privileged containers. * `network_mode` - (Optional) The network mode to be used for the container. In order to support userspace networking plugins in Docker 1.9 this accepts any value. The default is `bridge`. Other networking modes may not work without additional configuration on the host (which is outside the scope of Nomad). Valid values pre-docker 1.9 are `default`, `bridge`, `host`, `none`, or `container:name`. See below for more details. * `hostname` - (Optional) The hostname to assign to the container. When launching more than one of a task (using `count`) with this option set, every container the task starts will have the same hostname. * `dns_servers` - (Optional) A list of DNS servers for the container to use (e.g. ["8.8.8.8", "8.8.4.4"]). *Docker API v1.10 and above only* * `dns_search_domains` - (Optional) A list of DNS search domains for the container to use. * `port_map` - (Optional) A key/value map of port labels (see below). * `auth` - (Optional) Provide authentication for a private registry (see below). ### Container Name Nomad creates a container after pulling an image. Containers are named `{taskName}-{allocId}`. This is necessary in order to place more than one container from the same task on a host (e.g. with count > 1). This also means that each container's name is unique across the cluster. This is not configurable. ### Authentication If you want to pull from a private repo (for example on dockerhub or quay.io), you will need to specify credentials in your job via the `auth` option. The `auth` object supports the following keys: * `username` - (Optional) The account username. * `password` - (Optional) The account password. * `email` - (Optional) The account email. * `server_address` - (Optional) The server domain/ip without the protocol. Docker Hub is used by default. Example: ``` task "secretservice" { driver = "docker" config { image = "secret/service" auth { username = "dockerhub_user" password = "dockerhub_password" } } } ``` **Please note that these credentials are stored in Nomad in plain text.** Secrets management will be added in a later release. ## Networking Docker supports a variety of networking configurations, including using host interfaces, SDNs, etc. Nomad uses `bridged` networking by default, like Docker. You can specify other networking options, including custom networking plugins in Docker 1.9. **You may need to perform additional configuration on the host in order to make these work.** This additional configuration is outside the scope of Nomad. ### Allocating Ports You can allocate ports to your task using the port syntax described on the [networking page](/docs/jobspec/networking.html). Here is a recap: ``` task "webservice" { driver = "docker" port "http" {} port "https" {} } ``` ### Forwarding and Exposing Ports A Docker container typically specifies which port a service will listen on by specifying the `EXPOSE` directive in the `Dockerfile`. Because dynamic ports will not match the ports exposed in your Dockerfile, Nomad will automatically expose all of the ports it allocates to your container. These ports will be identified via environment variables. For example: ``` port "http" {} ``` If Nomad allocates port `23332` to your task for `http`, `23332` will be automatically exposed and forwarded to your container, and the driver will set an environment variable `NOMAD_PORT_http` with the value `23332` that you can read inside your container. This provides an easy way to use the `host` networking option for better performance. ### Using the Port Map If you prefer to use the traditional port-mapping method, you can specify the `port_map` option in your job specification. It looks like this: ``` task "redis" { driver = "docker" port "redis" {} config { image = "redis" port_map { redis = 6379 } } } ``` If Nomad allocates port `23332` to your task, the Docker driver will automatically setup the port mapping from `23332` on the host to `6379` in your container, so it will just work! Note that by default this only works with `bridged` networking mode. It may also work with custom networking plugins which implement the same API for expose and port forwarding. ### Networking Protocols The Docker driver configures ports on both the `tcp` and `udp` protocols. This is not configurable. ### Other Networking Modes Some networking modes like `container` or `none` will require coordination outside of Nomad. First-class support for these options may be improved later through Nomad plugins or dynamic job configuration. ## Host Requirements Nomad requires Docker to be installed and running on the host alongside the Nomad agent. Nomad was developed against Docker `1.8.2` and `1.9`. By default Nomad communicates with the Docker daemon using the daemon's unix socket. Nomad will need to be able to read/write to this socket. If you do not run Nomad as root, make sure you add the Nomad user to the Docker group so Nomad can communicate with the Docker daemon. For example, on ubuntu you can use the `usermod` command to add the `vagrant` user to the `docker` group so you can run Nomad without root: sudo usermod -G docker -a vagrant For the best performance and security features you should use recent versions of the Linux Kernel and Docker daemon. ## Agent Configuration The `docker` driver has the following [client configuration options](/docs/agent/config.html#options): * `docker.endpoint` - Defaults to `unix:///var/run/docker.sock`. You will need to customize this if you use a non-standard socket (http or another location). * `docker.auth.config` - Allows an operator to specify a json file which is in the dockercfg format containing authentication information for private registry. * `docker.tls.cert` - Path to the server's certificate file (`.pem`). Specify this along with `docker.tls.key` and `docker.tls.ca` to use a TLS client to connect to the docker daemon. `docker.endpoint` must also be specified or this setting will be ignored. * `docker.tls.key` - Path to the client's private key (`.pem`). Specify this along with `docker.tls.cert` and `docker.tls.ca` to use a TLS client to connect to the docker daemon. `docker.endpoint` must also be specified or this setting will be ignored. * `docker.tls.ca` - Path to the server's CA file (`.pem`). Specify this along with `docker.tls.cert` and `docker.tls.key` to use a TLS client to connect to the docker daemon. `docker.endpoint` must also be specified or this setting will be ignored. * `docker.cleanup.container` Defaults to `true`. Changing this to `false` will prevent Nomad from removing containers from stopped tasks. * `docker.cleanup.image` Defaults to `true`. Changing this to `false` will prevent Nomad from removing images from stopped tasks. * `docker.privileged.enabled` Defaults to `false`. Changing this to `true` will allow containers to use `privileged` mode, which gives the containers full access to the host's devices. Note that you must set a similar setting on the Docker daemon for this to work. `true` will also allow containers to run with ipc_mode, pid_mode and uts_mode set to `host`, which gives access to the hosts ipc, pid and UTS namespaces respectively. cert := d.config.Read("docker.tls.cert") key := d.config.Read("docker.tls.key") ca := d.config.Read("docker.tls.ca") Note: When testing or using the `-dev` flag you can use `DOCKER_HOST`, `DOCKER_TLS_VERIFY`, and `DOCKER_CERT_PATH` to customize Nomad's behavior. If `docker.endpoint` is set Nomad will **only** read client configuration from the config filie. An example is given below: ``` client { options = { "docker.cleanup.container" = "false" "docker.cleanup.image" = "false" } } ``` ## Agent Attributes The `docker` driver will set the following client attributes: * `driver.docker` - This will be set to "1", indicating the driver is available. * `driver.docker.version` - This will be set to version of the docker server ## Resource Isolation ### CPU Nomad limits containers' CPU based on CPU shares. CPU shares allow containers to burst past their CPU limits. CPU limits will only be imposed when there is contention for resources. When the host is under load your process may be throttled to stabilize QOS depending on how many shares it has. You can see how many CPU shares are available to your process by reading `NOMAD_CPU_LIMIT`. 1000 shares are approximately equal to 1Ghz. Please keep the implications of CPU shares in mind when you load test workloads on Nomad. ### Memory Nomad limits containers' memory usage based on total virtual memory. This means that containers scheduled by Nomad cannot use swap. This is to ensure that a swappy process does not degrade performance for other workloads on the same host. Since memory is not an elastic resource, you will need to make sure your container does not exceed the amount of memory allocated to it, or it will be terminated or crash when it tries to malloc. A process can inspect its memory limit by reading `NOMAD_MEMORY_LIMIT`, but will need to track its own memory usage. Memory limit is expressed in megabytes so 1024 = 1Gb. ### IO Nomad's Docker integration does not currently provide QOS around network or filesystem IO. These will be added in a later release. ### Security Docker provides resource isolation by way of [cgroups and namespaces](https://docs.docker.com/introduction/understanding-docker/#the-underlying-technology). Containers essentially have a virtual file system all to themselves. If you need a higher degree of isolation between processes for security or other reasons, it is recommended to use full virtualization like [QEMU](/docs/drivers/qemu.html).