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Garbage collection

Part of syncing a cluster with a git repository is getting rid of resources in the cluster that have been removed in the repository. You can tell fluxd to do this "garbage collection" using the command-line flag --sync-garbage-collection. It's important to know how it operates, and appreciate its limitations, before enabling it.

How garbage collection works

When garbage collection is enabled, syncing is done in two phases:

  1. Apply all the manifests in the git repo (as delimited by the branch and path arguments), and give each resource a label marking it as having been synced from this source.

  2. Ask the cluster for all the resources marked as being from this source, and delete those that were not applied in step 1.

In the above, "source" refers to the particular combination of git repo URL, branch, and paths that this fluxd has been configured to use, which is taken as identifying the resources under this fluxd's control.

We need to be careful about identifying these accurately, since getting it wrong could mean not deleting resources that should be deleted; or (much worse), deleting resources that are under another fluxd's control.

The definition of "source" affects how garbage collection behaves when you reconfigure fluxd. It is intended to be conservative: it ensures that fluxd will not delete resources that it did not create.

Limitations of this approach

In general, if you change an element of the source (the git repo URL, branch, and paths), there is a possiblility that resources no longer present in the new source will be missed (i.e., not deleted) by garbage collection, and you will need to delete them by hand.

Config change What happens
git URL or branch If the manifests at the new git repo are the same, they will all be relabelled, and things will proceed as usual. If they are different, the resources from the old repo will be missed by garbage collection and will need to be deleted by hand
path added Existing resources will be relabelled, and new resources (from manifests in the new path) will be created. Then things will proceed as usual.
path removed The resources from manifests in the removed path will be missed by garbage collection, and will need to be deleted by hand. Other resources will be treated as usual.