Handling stemcells

In Tanzu Operations Manager, every product uploaded and staged needs to be given a stemcell in order to operate. By default, every stemcell uploaded to Tanzu Operations Manager automatically associates with any new or existing products. Using the automation tasks, this default can be overridden to not have a stemcell associate with any products, and can be manually assigned as you deem necessary.

Why do your stemcell handling manually?

Unless there is a specific need to manually handle the stemcells in Tanzu Operations Manager, it is recommended that you use the default. A common use case for manual stemcell handling is updating the product stemcells one at a time to minimize downtime during Apply Changes. This is particularly beneficial in environments with large numbers of tiles that share the same stemcell.

How to use the stemcell handling tasks in automation

Platform Automation Toolkit has tasks for the manual handling of stemcells in Tanzu Operations Manager. These tasks, in order, are:

Follow these steps:

download-product: Create a config.yml for this task using the example provided.

After running the task, there will be a new file named assign-stemcell.yml. The task put a config file containing two values, product and stemcell, into the assign-stemcell-config output directory. This can be used with assign-stemcell to ensure that the latest stemcell is used with that product.
Run the upload-product and stage-product tasks to get the resources into Tanzu Operations Manager.
Run the upload-stemcell task.

To upload the stemcell to Tanzu Operations Manager without associating it with a product, execute the upload-stemcell task with the FLOATING_STEMCELL: false flag set.

Here is an example of this, in a pipeline:
```
- task: upload-stemcell
  image: platform-automation-image
  file: platform-automation-tasks/tasks/upload-stemcell.yml
  input_mapping:
    env: configuration
    stemcell: downloaded-stemcell
  params:
    ENV_FILE: ((foundation))/env/env.yml
    FLOATING_STEMCELL: false
```
Caution Do not run upload-stemcell until after the stage-product task has completed. When the two tasks are run in the opposite order, the stemcell still auto-associates with the product.
Run the assign-stemcell task to associate the stemcell with the staged product. If you are using the download-product task before doing this in the same job, you must assign the config using the input_mapping key to assign the outputted config to the config that assign-stemcell is expecting. Upon successful completion, the stemcell specified in the config will be associated with the product specified in the config, and no other product will be associated with that stemcell.

Here is an example of this, in a pipeline:
```
- task: assign-stemcell
  image: platform-automation-image
  file: platform-automation-tasks/tasks/assign-stemcell.yml
  input_mapping:
    env: configuration
    config: assign-stemcell-config
  params:
    ENV_FILE: ((foundation))/env/env.yml
```
Now you can run configure product and apply changes on the product as normal.

How to download a specific stemcell

Platform Automation Toolkit can be used to download a specific stemcell. To do this, create a config.yml for this task using the example provided in Task inputs and outputs.