--- 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 ```hcl task "webservice" { driver = "docker" config { image = "redis:3.2" labels { group = "webservice-cache" } } } ``` The `docker` driver supports the following configuration in the job spec. Only `image` is required. * `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. If the tag is omitted or equal to `latest` the driver will always try to pull the image. If the image to be pulled exists in a registry that requires authentication credentials must be provided to Nomad. Please see the [Authentication section](#authentication). ```hcl config { image = "https://hub.docker.internal/redis:3.2" } ``` * `args` - (Optional) A list of arguments to the optional `command`. If no `command` is specified, the arguments are passed directly to the container. References to environment variables or any [interpretable Nomad variables](/docs/runtime/interpolation.html) will be interpreted before launching the task. For example: ```hcl config { args = [ "-bind", "${NOMAD_PORT_http}", "${nomad.datacenter}", "${MY_ENV}", "${meta.foo}", ] } ``` * `auth` - (Optional) Provide authentication for a private registry (see below). * `auth_soft_fail` `(bool: false)` - Don't fail the task on an auth failure. Attempt to continue without auth. * `command` - (Optional) The command to run when starting the container. ```hcl config { command = "my-command" } ``` * `dns_search_domains` - (Optional) A list of DNS search domains for the container to use. * `dns_options` - (Optional) A list of DNS options for the container to use. * `dns_servers` - (Optional) A list of DNS servers for the container to use (e.g. ["8.8.8.8", "8.8.4.4"]). Requires Docker v1.10 or greater. * `extra_hosts` - (Optional) A list of hosts, given as host:IP, to be added to `/etc/hosts`. * `force_pull` - (Optional) `true` or `false` (default). Always pull latest image instead of using existing local image. Should be set to `true` if repository tags are mutable. * `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. * `interactive` - (Optional) `true` or `false` (default). Keep STDIN open on the container. * `sysctl` - (Optional) A key-value map of sysctl configurations to set to the containers on start. ```hcl config { sysctl { net.core.somaxconn = "16384" } } ``` * `ulimit` - (Optional) A key-value map of ulimit configurations to set to the containers on start. ```hcl config { ulimit { nproc = "4242" nofile = "2048:4096" } } ``` * `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 Docker containers started by Nomad 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. * `ipv4_address` - (Optional) The IPv4 address to be used for the container when using user defined networks. Requires Docker 1.13 or greater. * `ipv6_address` - (Optional) The IPv6 address to be used for the container when using user defined networks. Requires Docker 1.13 or greater. * `labels` - (Optional) A key-value map of labels to set to the containers on start. ```hcl config { labels { foo = "bar" zip = "zap" } } ``` * `load` - (Optional) Load an image from a `tar` archive file instead of from a remote repository. Equivalent to the `docker load -i ` command. ```hcl artifact { source = "http://path.to/redis.tar" } config { load = "redis.tar" image = "redis" } ``` * `logging` - (Optional) A key-value map of Docker logging options. The default value is `syslog`. ```hcl config { logging { type = "fluentd" config { fluentd-address = "localhost:24224" tag = "your_tag" } } } ``` * `mac_address` - (Optional) The MAC address for the container to use (e.g. "02:68:b3:29:da:98"). * `network_aliases` - (Optional) A list of network-scoped aliases, provide a way for a container to be discovered by an alternate name by any other container within the scope of a particular network. Network-scoped alias is supported only for containers in user defined networks ```hcl config { network_mode = "user-network" network_aliases = [ "${NOMAD_TASK_NAME}", "${NOMAD_TASK_NAME}-${NOMAD_ALLOC_INDEX}" ] } ``` * `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` for all operating systems but Windows, which defaults to `nat`. 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`. * `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. See below for more details. * `port_map` - (Optional) A key-value map of port labels (see below). * `security_opt` - (Optional) A list of string flags to pass directly to [`--security-opt`](https://docs.docker.com/engine/reference/run/#security-configuration). For example: ```hcl config { security_opt = [ "credentialspec=file://gmsaUser.json", ] } ``` * `shm_size` - (Optional) The size (bytes) of /dev/shm for the container. * `SSL` - (Optional) If this is set to true, Nomad uses SSL to talk to the repository. The default value is `true`. **Deprecated as of 0.5.3** * `tty` - (Optional) `true` or `false` (default). Allocate a pseudo-TTY for the container. * `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. * `userns_mode` - (Optional) `host` or not set (default). Set to `host` to use the host's user namespace when user namespace remapping is enabled on the docker daemon. * `volumes` - (Optional) A list of `host_path:container_path` strings to bind host paths to container paths. Mounting host paths outside of the allocation directory can be disabled on clients by setting the `docker.volumes.enabled` option set to false. This will limit volumes to directories that exist inside the allocation directory. ```hcl config { volumes = [ # Use absolute paths to mount arbitrary paths on the host "/path/on/host:/path/in/container", # Use relative paths to rebind paths already in the allocation dir "relative/to/task:/also/in/container" ] } ``` * `volume_driver` - (Optional) The name of the volume driver used to mount volumes. Must be used along with `volumes`. Using a `volume_driver` also allows to use `volumes` with a named volume as well as absolute paths. If `docker.volumes.enabled` is false then volume drivers are disallowed. ```hcl config { volumes = [ # Use named volume created outside nomad. "name-of-the-volume:/path/in/container" ] # Name of the Docker Volume Driver used by the container volume_driver = "flocker" } ``` * `work_dir` - (Optional) The working directory inside the container. * `mounts` - (Optional) A list of [mounts](https://docs.docker.com/engine/reference/commandline/service_create/#add-bind-mounts-or-volumes) to be mounted into the container. Only volume type mounts are supported. ```hcl config { mounts = [ { target = "/path/in/container" source = "name-of-volume" readonly = false volume_options { no_copy = false labels { foo = "bar" } driver_config { name = "flocker" options = { foo = "bar" } } } } ] } ``` * `devices` - (Optional) A list of [devices](https://docs.docker.com/engine/reference/commandline/run/#add-host-device-to-container-device) to be exposed the container. `host_path` is the only required field. By default, the container will be able to `read`, `write` and `mknod` these devices. Use the optional `cgroup_permissions` field to restrict permissions. ```hcl config { devices = [ { host_path = "/dev/sda1" container_path = "/dev/xvdc" cgroup_permissions = "r" }, { host_path = "/dev/sda2" container_path = "/dev/xvdd" } ] } ``` ### 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 in the task config. * by storing explicit repository credentials or by specifying Docker `credHelpers` in a file and setting the [docker.auth.config](#auth_file) value on the client. * by specifying a [docker.auth.helper](#auth_helper) on the client 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-config: ```hcl task "example" { driver = "docker" config { image = "secret/service" auth { username = "dockerhub_user" password = "dockerhub_password" } } } ``` Example docker-config, using two helper scripts in $PATH, "docker-credential-ecr" and "docker-credential-vault": ```json { "auths": { "internal.repo": { "auth": "`echo -n ':' | base64 -w0`" } }, "credHelpers": { ".dkr.ecr..amazonaws.com": "ecr-login" }, "credsStore": "secretservice" } ``` Example agent configuration, using a helper script "docker-credential-ecr" in $PATH ```hcl client { enabled = true options { "docker.auth.helper" = "ecr" } } ``` !> **Be Careful!** At this time 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/job-specification/network.html). Here is a recap: ```hcl task "example" { driver = "docker" resources { network { 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: ```hcl 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: ```hcl task "example" { driver = "docker" config { image = "redis" port_map { redis = 6379 } } resources { network { mbits = 20 port "redis" {} } } } ``` 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. ### Advertising Container IPs *New in Nomad 0.6.* When using network plugins like `weave` that assign containers a routable IP address, that address will automatically be used in any `service` advertisements for the task. You may override what address is advertised by using the `address_mode` parameter on a `service`. See [service](/docs/job-specification/service.html) for details. ### 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. ## Client 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. ## Client Configuration The `docker` driver has the following [client configuration options](/docs/agent/configuration/client.html#options): * `docker.endpoint` - If using a non-standard socket, HTTP or another location, or if TLS is being used, `docker.endpoint` must be set. If unset, Nomad will attempt to instantiate a Docker client using the `DOCKER_HOST` environment variable and then fall back to the default listen address for the given operating system. Defaults to `unix:///var/run/docker.sock` on Unix platforms and `npipe:////./pipe/docker_engine` for Windows. * `docker.auth.config` - Allows an operator to specify a JSON file which is in the dockercfg format containing authentication information for a private registry, from either (in order) `auths`, `credHelpers` or `credsStore`. * `docker.auth.helper` - Allows an operator to specify a [credsStore](https://docs.docker.com/engine/reference/commandline/login/#credential-helper-protocol) -like script on $PATH to lookup authentication information from external sources. The script's name must begin with `docker-credential-` and this option should include only the basename of the script, not the path. * `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.image` Defaults to `true`. Changing this to `false` will prevent Nomad from removing images from stopped tasks. * `docker.cleanup.image.delay` A time duration, as [defined here](https://golang.org/pkg/time/#ParseDuration), that defaults to `3m`. The delay controls how long Nomad will wait between an image being unused and deleting it. If a tasks is received that uses the same image within the delay, the image will be reused. * `docker.volumes.enabled`: Defaults to `true`. Allows tasks to bind host paths (`volumes`) inside their container and use volume drivers (`volume_driver`). Binding relative paths is always allowed and will be resolved relative to the allocation's directory. * `docker.volumes.selinuxlabel`: Allows the operator to set a SELinux label to the allocation and task local bind-mounts to containers. If used with `docker.volumes.enabled` set to false, the labels will still be applied to the standard binds in the container. * `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. 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 file. An example is given below: ```hcl client { options { "docker.cleanup.image" = "false" } } ``` ## Client 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.bridge_ip` - The IP of the Docker bridge network if one exists. * `driver.docker.version` - This will be set to version of the docker server. Here is an example of using these properties in a job file: ```hcl job "docs" { # Require docker version higher than 1.2. constraint { attribute = "${driver.docker.version}" operator = ">" version = "1.2" } } ``` ## 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 1 GHz. 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 = 1 GB. ### 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). ## Docker for Mac Caveats Docker for Mac runs Docker inside a small VM and then allows access to parts of the host filesystem into that VM. At present, nomad uses a syslog server bound to a Unix socket within a path that both the host and the VM can access to forward log messages back to nomad. But at present, Docker For Mac does not work for Unix domain sockets (https://github.com/docker/for-mac/issues/483) in one of these shared paths. As a result, using nomad with the docker driver on OS X/macOS will work, but no logs will be available to nomad. Users must use the native docker facilities to examine the logs of any jobs running under docker. In the future, we will resolve this issue, one way or another. ## Docker for Windows Caveats Docker for Windows only supports running Windows containers. Because Docker for Windows is relatively new and rapidly evolving you may want to consult the [list of relevant issues on GitHub][WinIssues]. [WinIssues]: https://github.com/hashicorp/nomad/issues?q=is%3Aopen+is%3Aissue+label%3Adriver%2Fdocker+label%3Aplatform-windows