Stemcells

In order to manage BOSH stemcells in anynines-deployment, we've made stemcells configurable via the IAAS config. We configure a list of stemcells in iaas.stemcells (see config/iaas-config.yml.example for an example). This has the benefit of having all stemcells configured in one location and having it referenced anywhere it's needed. It also allows to use one type of stemcell in the services and another in the service instances. You can also use ops files to configure a certain type of stemcells for a particular component. This gives you a lot of control while preserving DRY principles by using sensible defaults.

Currently, Ubuntu Jammy is the default stemcell for all services and service instances. This can be changed to any OS supported by anynines-deployment.

Note 1: In general, we no longer support Ubuntu Xenial.

Note 2: In the case of the a9s Billing component, Ubuntu Bionic is not supported. The stemcell Ubuntu Xenial at version 621.125 is used as an exception.

Currently supported stemcells

We currently support the Ubuntu Jammy and Ubuntu Bionic stemcells on supported CPIs.

We've tested the following versions on our test system:

Linux stemcells	Versions	Comment
Ubuntu Jammy	1.486	Except: a9s PostgreSQL 11, a9s PostgreSQL 10
Ubuntu Bionic	1.204
Ubuntu Xenial	621.125	a9s Billing

Changing the default stemcell

danger

Before changing the default Stemcell for existing a9s PostgreSQL 13 instances, carefully read this documentation: Updating a9s PostgreSQL 13 to Jammy Stemcell.

We use YAML anchors to create a reference to a particular stemcell and use that reference throughout the IAAS config file. Please find the string &a9s-stemcell-default in the IAAS config file (example: config/iaas-config.yml.example) and "move" the string (a so called YAML anchor) to another stemcell. You can also introduce a different stemcell below the stemcell that uses this YAML anchor and assign it the YAML anchor &a9s-stemcell-default. After that, the default stemcell will be the one you configured.

An example for your IaaS config:

iaas:
  stemcells:
    ubuntu-xenial: &a9s-stemcell-xenial
      os: ubuntu-xenial
      alias: ubuntu-xenial
      version: 621.125
      sha1: 7724ce4272dd8f19b44584a17d31595eac7595e5
    ubuntu-jammy: &a9s-stemcell-default
      os: ubuntu-jammy
      alias: ubuntu-jammy
      version: 1.486
      sha1: d3628c345f1979bdc003effbb547616f593ed6fb

You can then reference such a stemcell like e.g.:

logme2_service:
  stemcells:
    service: *a9s-stemcell-default

If you want to use a different stemcell or even stemcell version in your service instances only, you can do so by using an Ops file. Please find an example in ops/replace-stemcell-template-uploader.yml You might have to create your own copy of that Ops file with the correct values for your setup.

Example IAAS config

The following YAML text is an example IAAS configuration. It introduces two stemcells (Ubuntu Xenial and Ubuntu Bionic) and allows referring to them by using the YAML anchors (&a9s-stemcell-default and &a9s-stemcell-xenial).

iaas:
  stemcells:
    ubuntu-xenial: &a9s-stemcell-xenial
      os: ubuntu-xenial
      alias: ubuntu-xenial
      version: 621.125
      sha1: 7724ce4272dd8f19b44584a17d31595eac7595e5
    ubuntu-jammy: &a9s-stemcell-default
      os: ubuntu-jammy
      alias: ubuntu-jammy
      version: 1.486
      sha1: d3628c345f1979bdc003effbb547616f593ed6fb

In order to refer to them, you can use a YAML alias:

iaas:
  data_service:
    stemcell: *a9s-stemcell-default

Once you introduced the anchors and an alias, you can refer to these stemcells in different ways:

stemcells:
- os: ((iaas.data_service.stemcells.service.os))
  alias: ((iaas.data_service.stemcells.service.alias))
  version: ((iaas.data_service.stemcells.service.version))

- name: jobname
  vm_type: small
  instances: 1
  azs: [z1, z2, z3]
  stemcell: ((iaas.data_service.stemcells.service.alias))
  jobs:
  - { name: jobname, release: jobrelease }
  properties:
    ...