Kubernetes Tutorial: Merge all the Kubeconfigs! [Part 7]

Once you start managing more than one Kubernetes cluster, you'll start to demand more from your 

$KUBECONFIG

. Early on in my career spinning pods, I kept a separate 

.kubeconfig

 file for each cluster, and wrote a small shell function to set the requisite environment variables. To switch between clusters was as simple as:

I did this because the "correct" command was too much to remember:See what I mean?Then I met kubectx and kubens, and they quickly became invaluable.

Now I've got this directory full of all these disparate, discrete configuration files, and I don't want to hand-edit them back together. Thankfully,

kubectl

 itself can merge them for us!

Note: 

kubectl

 will only merge configuration files if you specify them via the 

$KUBECONFIG

 environment variable. You cannot use the

--kubeconfig

 command-line flag, it won't work.

To demonstrate this, I'm going to show you my 

~/.k

 directory:

Using 

kubectl config get-contexts

 commands, we can see that each of them is different:

If you put two (or more) files, separated by colons, in 

$KUBECONFIG

, then

kubectl

 will merge them together semantically, and operate on the composite configuration. Any changes you make, like changing namespaces or setting contexts, will update the appropriate member file(s).

To write a new, aggregate configuration that contains the results of the merge, we can use 

kubectl config view --raw

. The 

--raw

 flag prevents 

kubectl

 from redacting user secrets, certificates, and keys. To save this combined file, we can employ some shell redirection, along with a bit of caution.

Every UNIX shell I've ever used truncates files that are the target of 

>

-style output redirection, before the command producing the output gets executed. It's the nature of UNIX pipelines. We have to be careful with the order of our operations.

This will fail spectacularly (and most assuredly destroy data in the process!):

The 

a

 configuration file will be empty by the time 

kubectl

 gets around to trying to merge it in with the other two. Instead, use a temporary file and a rename operation:

Pro Tip: While you are merging all of these configurations together, you can also embed any referenced, external files (like certificates and private keys) by swapping out the 

--raw

 flag for 

--flatten

. This produces "portable" kubeconfigs, which do not have any dependencies on other parts of your filesystem. They can be moved, or copied, without losing their utility.

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