Adding a custom stack

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This topic describes how to add a custom stack under the Diego architecture. To add a stack, you first build a BOSH job template that installs the stack on the host machine. Then you configure your deployment manifests so that Cloud Foundry can run the job when it creates cells.

The Cloud Foundry cflinuxfs4 repository contains scripts for building your own custom stacks, as well as the available Cloud Foundry stacks.

The following example adds a new Linux-based pancakes stack for use with the Garden-runC operating system. This pancakes stack could, for example, support applications that require an old version of CentOS or Ubuntu.

Step 1: Create a BOSH job template

Stacks exist in a subdirectory on their host machine, typically under /var/vcap/packages or /var/vcap/data. Your BOSH job template must deploy the stack onto a host machine, and provide lifecycle binaries that work with your stack. The lifecycle binaries for your stack are helper programs that stage and run apps on the stack file system. To create a pancakes-release job template that deploys a custom stack, follow these steps:

1. Create a BOSH release pancakes-release for a job template that expands a stack into place in its subdirectory. The rootfs must be packaged as a .tar file, for example, a pancakes-rootfs template might create a tarred full Linux root file system at /var/vcap/packages/pancakes-rootfs/rootfs.tar. See the rootfses job template in diego-release for one way to do this.

2. Create lifecycle binaries for your stack. See the diego-release repository for examples of app lifecycle binary source code:

   • Buildpack app lifecycle
   • Docker app lifecycle
   • Windows app lifecycle

3. Generate a gzipped tar archive of the lifecycle binaries, pancakes-app-lifecycle.tgz.

4. Create a dummy pancakes-app-lifecycle job template as a package within pancakes-release. Include the pancakes-app-lifecycle.tgz file in the job template directory.

Note The pancakes-app-lifecycle job template does not need to run any process of its own.

1. List the dummy pancakes-app-lifecycle job as a dependency in the pancakes-release spec file. This makes BOSH publish the lifecycle binaries to /var/vcap/packages for inclusion in any cells that use the pancakes stack.

Step 2: Update the manifests

1. Add the pancakes-rootfs job and release name to the Diego manifest, to the list of job templates defined for the cell object under base_job_templates. This makes the expanded rootfs available locally on the Diego Cell, at /var/vcap/packages/pancakes-rootfs/rootfs. For example, in the manifests generated with the spiff-based tooling in diego-release, add the lines shown in bold to the following list of cell job templates:

   cell:
    - name: rep
       release: diego
     - name: garden
       release: garden-runc
     - name: rootfses
       release: diego
     - name: pancakes-rootfs
       release: pancakes
     - name: metron_agent
       release: cf
   

2. Add pancakes-app-lifecycle to the base_job_templates list under the file_server Diego job. In diego-release, the file_server job resides in the access job template group. For example, add the lines shown in bold to the following list of job templates:

   access:
    - name: ssh_proxy
      release: diego
    - name: metron_agent
      release: cf
    - name: file_server
      release: diego
    - name: pancakes-app-lifecycle
      release: pancakes
   

3. The diego.rep.preloaded_rootfses property of the Cell Rep holds an array associating stacks with the location of their tarred rootfs in the filesystem. Add a pair to this list to associate the pancakes stack with its file system root location, set up on the cell by the pancakes-rootfs job. For example, in the preloaded_rootfses: property under rep: in your Diego manifest, set the array to the following by adding the text shown in bold:

     ["cflinuxfs3:/var/vcap/packages/cflinuxfs3/rootfs.tar",
     "pancakes:/var/vcap/packages/pancakes-rootfs/rootfs.tar"]
   

4. Configure the stager and nsync components to use the pancakes lifecycle binary bundle to start and stop apps running on the pancakes stack. For example, in CAPI release, add the line shown in bold to the default list under the manifest definitions for both diego.nsync.lifecycle_bundles and diego.stager.lifecycle.bundles:

     description: "List of lifecycle bundles arguments for different stacks in form 'lifecycle-name:path/to/bundle'"
     default:
       - "buildpack/cflinuxfs3:buildpack_app_lifecycle/buildpack_app_lifecycle.tgz"
       - "buildpack/pancakes:pancakes-app-lifecycle/pancakes-app-lifecycle.tgz"
       - "buildpack/windows2012R2:windows_app_lifecycle/windows_app_lifecycle.tgz"
       - "docker:docker_app_lifecycle/docker_app_lifecycle.tgz"
   

5. Configure the Cloud Controller for the new stack by adding it to the cc.stacks property in the CF manifest. For example, in the diego-release manifest generation stubs for CF, add the lines shown in bold:

   properties:
     cc:
       stacks:
         - name: "cflinuxfs3"
           description: "Cloud Foundry Linux-based filesystem"
         -  name: "windows2012R2"
           description: "Windows Server 2012 R2"
         - name: "pancakes"
           description: "Linux-based filesystem, with delicious pancakes"