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Docker Support
Concord supports running Docker images within a process flow.
Usage
Short syntax:
flows:
default:
- docker: library/alpine
cmd: echo '${greeting}'
configuration:
arguments:
greeting: "Hello, world!"
Using the task syntax:
flows:
default:
- task: docker
in:
image: library/alpine
cmd: echo '${greeting}'
configuration:
arguments:
greeting: "Hello, world!"
The above invocations are 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);stdoutandstderr- optional, string. Name of variables to save the stdout and stderr of the container;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:
- docker: library/alpine
cmd: cd /usr/ && echo "I'm in $PWD"
To run multiple commands multiline YAML strings can be used:
- docker: 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:
- docker: 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:
- docker: library/alpine
cmd: echo $GREETING
envFile: "myEnvFile"
The path must be relative to the process’ working directory ${workDir}.
It is an equivalent of running docker run --env-file=myEnvFile.
Docker options
Add Host Option
Additional /etc/hosts lines can be specified using hosts parameter:
flows:
default:
- docker: library/alpine
cmd: echo '${greeting}'
hosts:
- foo:10.0.0.3
- bar:10.7.3.21
configuration:
arguments:
greeting: "Hello, world!"
Capturing the Output
The stdout and stderr parameters can be used to capture the output of
commands running in the Docker container:
- docker: library/alpine
cmd: echo "Hello, Concord!"
stdout: myOut
- log: "Got the greeting: ${myOut.contains('Hello')}"
In the example above the output (stdout) of the command running in the
container is not printed out into the log, but instead saved as myOut
variable.
The stderr parameter can be used to capture the errors of commands running
in the Docker container:
- docker: library/alpine
cmd: echo "Hello, ${name}" && (>&2 echo "STDERR WORKS")
stderr: myErr
- log: "Errors: ${myErr}"
In the example above the errors (stderr) of the command running in the
container is not printed out into the log, but instead saved as myErr
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.
