The Shell Grain

The Shell grain is an asset-agnostic grain that allows you to run bash/python3 commands as part of your environment’s launch and/or teardown. It’s useful if you need to prepare or clean up your environment’s cloud infrastructure as part of the deployment. For example, you could use this grain to run "datree" validations on a Kubernetes grain’s asset, or perhaps back up/clone a DB before environment deployment.

grains:
  validate:
    kind: shell
    spec:
      agent:
        name: …
      activities:
        deploy:
          commands:
            - …
        destroy:
          commands:
            - …

Agent

Please see the grain agent for more details.

Tools and Technologies

The following tools and technologies are installed out of the box on our agents in the Kubernetes pods and can be used when writing grain scripts (pre/post, etc.):

• dotnet
• python3
• pip3

Inputs

Similar to blueprint inputs, inputs provided to the Shell grain are used when launching the shell. Unlike other grains, in the Shell grain, inputs are used inside the commands section, wrapped in double curly brackets - " {{ .inputs.input1 }}".

grains:
  validate:
    kind: shell
    spec:
      agent:
        name: kubernetes-testing1
      activities:
        deploy:
          commands:
            - "apt-get -y install git unzip curl"
            - "git clone {{ .inputs.repoUrl }}"

Outputs

The Shell grain output can be captured during the shell execution and than be used as a blueprint output or as input for another grain. Note that the Shell grain output is the entire stdout of the grain execution.

outputs:
  deploy-output:
    value: '{{.grains.grain1.activities.deploy.commands.bash.output}}'

grains:
  grain1:
    kind: shell
    spec:
      files:
      - path: "dependencies/script.sh"
        source: shell-example
      agent:
      # The Torque agent that will be used to provision the environment.
        name: '{{ .inputs.agent }}'
      activities:
        deploy:
          commands:
            - name: bash
              command: "./script.sh"

Commands

The commands section allows to execute bash/python3 code or files stored in one of the space's repositories as part of the launch and/or end of the environment. The Shell grain has two command types - deploy for running code at the launch of the environment, and destroy for running code as part of the environment’s teardown.

grains:
  validate:
    kind: shell
    spec:
      agent:
        name: kubernetes-testing1
      activities:
        deploy:
          commands:
            - "apt-get -y install git unzip curl"
            - "git clone {{ .inputs.repoUrl }}"
            - "curl https://get.datree.io | /bin/bash"
            - "datree test {{.inputs.repoName}}/{{.inputs.filePath}}"
        destroy:
          commands:
            - "https://gist.githubusercontent.com/.../check.py"
            - "python3 check.py"

⚠️ Warning Each command new line from the above example is segregated in its own shell, so running these commands:

      activities:
       deploy:
         commands:
           - "cd /home"
           - "cat file.txt"

Would not work as expected. The correct syntax would be:

      activities:
       deploy:
         commands:
           - "cd /home; cat file.txt"

Another option would be to have a script file and call it directly only on one line.

Note: only the last command or script provided is evaluated for a successful exit code, all previous commands or scripts will still be ran regardless of failures.

note

You can specify the code to be run as free text bash/python3 commands or by referencing a file (any file type can be run, not just bash or python3).

To run a file, specify the file and its repo in the files section and the file name and extension under commands. For example, file "post-install-script.sh":

grains:
  validate:
    kind: shell
    spec:
      agent:
        name: ...
      files:
        - path: "scripts/post-install-script.sh"
          source: my-repo
      activities:
        deploy:
          commands:
            - "apt-get -y install git unzip curl"
            - "git clone {{ .inputs.repoUrl }}"
            - "curl https://get.datree.io | /bin/bash"
            - "./post-install-script.sh"
            - name: generate_report
              command: "datree test {{.inputs.repoName}}/{{.inputs.filePath}}"

Python 3 example:

commands
  - "apt-get -y install wget"
  - "wget https://.../check.py"
  - "python3 check.py"

Bash example:

commands
  - "apt-get -y install wget"
  - "wget https://.../simple.sh"
  - "/bin/bash simple.sh"