Diff strategies

Tanka supports two different ways of computing differences between the local configuration and the live cluster state: Either native kubectl diff -f - is used, which gives the best possible results, but is only possible for clusters with server-side diff support (Kubernetes 1.13+).

When this is not available, Tanka falls back to subset mode.

You can specify the diff-strategy to use on the command line as well:

# native
tk diff --diff-strategy=native .

# validate: Like native but with a server-side validation
tk diff --diff-strategy=validate .

# server-side
tk diff --diff-strategy=server .

# subset
tk diff --diff-strategy=subset .

Native

The native diff mode is recommended, because it uses kubectl diff underneath, which sends the objects to the Kubernetes API server and computes the differences over there.

This has the huge benefit that all possible changes by webhooks and other internal components of Kubernetes can be encountered as well.

However, this is a fairly new feature and only available on Kubernetes 1.13 or later. Only the API server (master nodes) needs to have that version, worker nodes do not matter.

There is a known issue with kubectl diff, which affects ports configured to use both TCP and UDP.

Server-side diffs

There are two additional modes which extend native: validate and server. While all kubectl diff commands are sent to the API server, these two methods take advantage of an additional server-side diff mode (which uses the kubectl diff --server-side flag, complementing the server-side apply mode).

Since a plain server diff often produces cruft, and wouldn’t be representative of a client-side apply, the validate method allows the server-side diff to check that all models are valid server-side, but still displays the native diff output to the user.

Subset

If native diffing is not supported by your cluster, Tanka provides subset diff as a fallback method.

Subset diff only compares fields present in the local configuration and ignores all other fields. When you remove a field locally, you will see no differences.

This is required, because Kubernetes adds dynamic fields to the state during runtime, which we cannot know of on the client side. To produce a somewhat usable output, we can effectively only compare what we already know about.

If this is a problem for you, consider switching to native mode.

External diff utilities

You can use external diff utilities by setting the environment variable KUBECTL_EXTERNAL_DIFF. If you want to use a GUI or interactive diff utility you must also set KUBECTL_INTERACTIVE_DIFF=1 to prevent Tanka from capturing stdout.