Home > docs > plugins v2 > Docker Support
Docker Support
Concord supports running Docker images within a process flow.
- Usage
- Parameters
- Environment Variables
- Docker Options
- Capturing the Output
- Custom Images
- Limitations
Usage
The docker task is called with standard
runtime-v2 task call syntax.
flows:
default:
- task: docker
in:
image: library/alpine
cmd: echo '${greeting}'
out: dockerResult
configuration:
arguments:
greeting: "Hello, world!"
The above invocation is equivalent to running
docker pull library/alpine && \
docker run -i --rm \
-v /path/to/process/workDir:/workspace \
library/alpine \
echo 'Hello, world!'
Parameters
image- mandatory, string. Docker image to use;cmd- optional, string. Command to run. If not specified, the image’sENTRYPOINTis used;env- optional, environment variables;envFile- optional. Path to the file containing environment variables;hosts- optional. Additional /etc/host entries;forcePull- optional, boolean. IftrueConcord runsdocker pull ${image}before starting the container. Default istrue;debug- optional, boolean. IftrueConcord prints out additional information into the log (the command line, parameters, etc);redirectErrorStream- optional boolean. Redirect container error output to standard output. Default isfalse;logOut- optional boolean. Sends container standard output to Concord process logs. Default istrue;logErr- optional boolean. Sends container error output to Concord process logs. Default istrue;saveOut- optional boolean. Save container standard output in task result, asstdoutvariable. Default isfalse;saveErr- optional boolean. Save container error output in task result, asstderrvariable. Default isfalse;pullRetryCount- optional, number. Number of retries ifdocker pullfails. Default is3;pullRetryInterval- optional, number. Delay in milliseconds betweendocker pullretries. Default is10000.
Note: The current process’ working directory is mounted as /workspace.
Concord replaces the container’s WORKDIR with /workspace. Depending
on your setup, you may need to change to a different working directory:
- task: docker
in:
image: library/alpine
cmd: cd /usr/ && echo "I'm in $PWD"
To run multiple commands multiline YAML strings can be used:
- task: docker
in:
image: library/alpine
cmd: |
echo "First command"
echo "Second command"
echo "Third command"
Concord automatically removes the container when the command is complete.
Environment Variables
Additional environment variables can be specified using env parameter:
flows:
default:
- task: docker
in:
image: library/alpine
cmd: echo $GREETING
env:
GREETING: "Hello, ${name}!"
configuration:
arguments:
name: "concord"
Environment variables can contain expressions: all values will be converted to strings.
A file containing environment variables can be used by specifying
the envFile parameter:
flows:
default:
- task: docker
in:
image: library/alpine
cmd: echo $GREETING
envFile: "myEnvFile"
The path must be relative to the process’ working directory ${workDir}.
It is an equivalent of running docker run --env-file=myEnvFile.
Docker options
Add Host Option
Additional /etc/hosts lines can be specified using hosts parameter:
flows:
default:
- task: docker
in:
image: library/alpine
cmd: echo '${greeting}'
hosts:
- foo:10.0.0.3
- bar:10.7.3.21
configuration:
arguments:
greeting: "Hello, world!"
Capturing the Output
The stdout and stderr attributes of the task’s returned data can be used to
capture the output of commands running in the Docker container:
- task: docker
in:
image: library/alpine
cmd: echo "Hello, Concord!"
saveOut: true
out: dockerResult
- log: "Got the greeting: ${dockerResult.stdout.contains('Hello')}"
In the example above, the output (stdout) of the command running in the
container is accessible in the returned object’s stdout attribute.
The stderr parameter can be used to capture the errors of commands running
in the Docker container:
- task: docker
in:
image: library/alpine
cmd: echo "Hello, ${name}" && (>&2 echo "STDERR WORKS")
saveErr: true
out: dockerResult
- log: "Errors: ${dockerResult.stderr}"
In the example above the errors (stderr) of the command running in the
container is accessible in the returned object’s stderr variable.
Custom Images
Currently, there’s only one requirement for custom Docker images: all images
must provide a standard POSIX shell as /bin/sh.
Limitations
Running containers as root user is not supported - all user containers are
executed using the concord user equivalent to a run command like docker run
-u concord ... myImage. The user is created automatically with UID 456.
As a result any operations in the docker container that require root access, such as installing packages, are not supported on Concord. If required, ensure that the relevant package installation and other tasks are performed as part of your initial container image build and published to the registry from which Concord retrieves the image.
