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---
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.
* `entrypoint` - (Optional) A string list overriding the image's entrypoint.
* `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 <filename>` 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 = "pxd"
}
```
* `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 = "pxd"
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"
}
]
}
```
* `cap_add` - (Optional) A list of Linux capabilities as strings to pass directly to
[`--cap-add`](https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities).
Effective capabilities (computed from `cap_add` and `cap_drop`) have to match the configured whitelist.
The whitelist can be customized using the `docker.caps.whitelist` key in the client node's configuration.
For example:
```hcl
config {
cap_add = [
"SYS_TIME",
]
}
```
* `cap_drop` - (Optional) A list of Linux capabilities as strings to pass directly to
[`--cap-drop`](https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities).
Effective capabilities (computed from `cap_add` and `cap_drop`) have to match the configured whitelist.
The whitelist can be customized using the `docker.caps.whitelist` key in the client node's configuration.
For example:
```hcl
config {
cap_drop = [
"MKNOD",
]
}
```
* `cpu_hard_limit` - (Optional) `true` or `false` (default). Use hard CPU
limiting instead of soft limiting. By default this is `false` which means
soft limiting is used and containers are able to burst above their CPU limit
when there is idle capacity.
* `cpu_cfs_period` - (Optional) An integer value that specifies the duration in microseconds of the period
during which the CPU usage quota is measured. The default is 100000 (0.1 second) and the maximum allowed
value is 1000000 (1 second). See [here](https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/resource_management_guide/sec-cpu#sect-cfs)
for more details.
* `advertise_ipv6_address` - (Optional) `true` or `false` (default). Use the container's
IPv6 address (GlobalIPv6Address in Docker) when registering services and checks.
See [IPv6 Docker containers](/docs/job-specification/service.html#IPv6 Docker containers) for details.
* `readonly_rootfs` - (Optional) `true` or `false` (default). Mount
the container's filesystem as read only.
* `pids_limit` - (Optional) An integer value that specifies the pid limit for
the container. Defaults to unlimited.
### 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 '<username>:<password>' | base64 -w0`" }
},
"credHelpers": {
"<XYZ>.dkr.ecr.<region>.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` <a id="auth_file"></a>- 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` <a id="auth_helper"></a>- 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.
* `docker.caps.whitelist`: A list of allowed Linux capabilities. Defaults to
`"CHOWN,DAC_OVERRIDE,FSETID,FOWNER,MKNOD,NET_RAW,SETGID,SETUID,SETFCAP,SETPCAP,NET_BIND_SERVICE,SYS_CHROOT,KILL,AUDIT_WRITE"`,
which is the list of capabilities allowed by docker by default, as
[defined here](https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities).
Allows the operator to control which capabilities can be obtained by
tasks using `cap_add` and `cap_drop` options. Supports the value `"ALL"` as a
shortcut for whitelisting all capabilities.
* `docker.cleanup.container`: Defaults to `true`. This option can be used to
disable Nomad from removing a container when the task exits. Under a name
conflict, Nomad may still remove the dead container.
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
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