Progress of the support of shell completion for the "kubectl cert-manager" plugin, coming in Kubernetes 1.24

[maelvls]

Currently, the only way to get shell completion to work when using the cert-manager kubectl plugin is to skip the kubectl plugin mechanism altogether as it can be read on the Kubectl plugin:

While the kubectl plugin is supported, it is recommended to use cmctl as this enables a better experience via tab auto-completion.

In the last couple of weeks, there has been a promising effort for bringing completion support to kubectl plugins. Marc Khouzam proposed the kubectl PR 105867. Cobra also v1.3.0 comes a fix to get flag completion, see below explanation. These two changes should land in kubectl probably in Kubernetes 1.24.

Here is what the completion will look like:

This issue tracks the progress of the kubectl plugin support for kubectl cert-manager.

Plan:

• Start discussing on this issue the best way of dealing with the "shim" -> as part of the documentation? Or installed by krew?
• Wait until Kubernetes 1.24 is released, at which point Shell completion for plugins kubernetes/kubernetes#105867 should have been merged.
• (non-blocking) Wait for the flag bug to be fixed, kubernetes/kubernetes must start using the next release of Cobra which has not been released yet.

Try the completion!

🚧 Last update to the below command lines: 14 January 2022.

If you would like to test the completion support:

1. Add ~/bin to your PATH. (optional, but the following steps assume that ~/bin is in your PATH).

   export PATH="$HOME/bin:$PATH"

2. Install the patched kubectl (kubectl PR 105867 + replace cobra v1.2.1 with v1.3.0 to get PR 1161):

   curl -L https://github.com/kubernetes/kubernetes/archive/d50260c72595d8bda78dbb02d1db847477f34a7e.tar.gz | tar xz  -C /tmp
   pushd /tmp/kubernetes-d50260c72595d8bda78dbb02d1db847477f34a7e
   go get github.com/spf13/cobra@v1.3.0
   go mod edit -replace github.com/spf13/cobra=github.com/spf13/cobra@v1.3.0
   go build -o ~/bin/kubectl -mod=mod ./cmd/kubectl
   popd

3. Install the kubectl cert-manager plugin:

    curl -SL https://github.com/jetstack/cert-manager/releases/download/v1.6.1/kubectl-cert_manager-linux-amd64.tar.gz | tar xzv kubectl-cert_manager && mv kubectl-cert_manager ~/bin

4. Enable cert-manager plugin completion by creating the shim kubectl_complete-cert_manager:

   # The following command assumes that ~/bin is in your PATH.
   cat <<'EOF' >~/bin/kubectl_complete-cert_manager && chmod u+x ~/bin/kubectl_complete-cert_manager
   #!/usr/bin/env sh
   # https://github.com/kubernetes/kubernetes/pull/105867
   kubectl cert-manager __complete "$@"
   EOF

Kubectl, Cobra v1.2.1 vs. v1.3.0 and the flag completion bug

Currently, kubectl using PR 105867 does not support flag completion. When completing flags for a plugin such as cert-manager, you can see that nothing appears when completing:

$ kubectl cert-manager status certificate -n<TAB><TAB>
# Nothing happens.

A fix for this bug was already merged in Cobra in PR 1161 released in cobra v1.3.0, and kubectl's go.mod still refers to cobra v1.2.1. In order to have the fix working, you need to update kubectl's go.mod to point cobra to v1.3.0.

Then, you should see:

$ kubectl cert-manager status certificate -n<TAB><TAB>
--as                            -- Username to impersonate for the operation
--as-group                      -- Group to impersonate for the operation, this flag can be repeated to specify multiple groups.
--cache-dir                     -- Default cache directory
--certificate-authority         -- Path to a cert file for the certificate authority
--client-certificate            -- Path to a client certificate file for TLS
...

/kind feature
/area ctl

[maelvls]

Updates:

• The kubectl_complete-<plugin> solution suggested by Marc Khouzam seems to have been lazily accepted in Command line completion for kubectl plugins kubernetes/kubernetes#74178.
• The update to Cobra 1.3.0 should be merged soon, see Update Cobra from 1.2.1 to 1.3.0 kubernetes/kubernetes#107628.
• My estimation is that kubectl 1.24 will be compatible with subcommand completion.

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[marckhouzam]

It took longer but the support for completion for plugins has been merged and will be part of kubectl 1.26.
kubernetes/kubernetes#105867

[maelvls]

Kubernetes 1.26 was released a few days ago, which means you can now use the kubectl cert-manager completion out-of-the-box! There is still a manual action required to enable the auto-completion though:

# The following command assumes that ~/bin is in your PATH.
cat <<'EOF' >~/bin/kubectl_complete-cert_manager && chmod u+x ~/bin/kubectl_complete-cert_manager
#!/usr/bin/env sh
# https://github.com/kubernetes/kubernetes/pull/105867
kubectl cert-manager __complete "$@"
EOF

My hope is that we will embed this kubectl_complete-cert_manager file to our Krew (kubernetes-sigs/krew#812) installation. Regarding Homebrew, the name of the formula is cmctl and the completion script is already shipped under this name.

Update: the above command is now officially documented in https://cert-manager.io/docs/reference/cmctl/#auto-completion-with-the-kubectl-plugin.