Use ClusterIP service name for connecting to memcached

[stefanprodan]

• add an option to replace memcached headless service with ClusterIP in Helm chart
• make Flux use the memcached ClusterIP name instead of SRV records when the memcached-service is set to string empty

Fix: #1591

Test image: stefanprodan/flux:mem-v5

PS. This is a breaking change in the Helm chart, using the new image with the old chart will not work since the old chart deploys memcached with a headless service

[squaremo]

his is a breaking change in the Helm chart,

.. and probably in most people's deployments, for the same reason. This ought to require a change in arguments, so it doesn't break when the image is updated.

[squaremo]

I suggest making it possible to tell fluxd to use the FixedServerMemcacheClient instead (and changing the example manifests and chart so they do that). Otherwise, this is a change that will break every deployment of fluxd.

[squaremo]

There's no need to change this; Use FixedServerMemcacheClient instead.

[squaremo]

Looks right to me -- does it work? :-)

[squaremo]

Well caught

[stefanprodan]

I've installed the chart with ClusterIP on and off, both are working fine. There is one caveat with helm upgrade since the ClusterIP field is immutable.

The upgrade fails with:

Error: UPGRADE FAILED: Service "flux-memcached" is invalid: spec.clusterIP: Invalid value: "": field is immutable

In order to fix the upgrade you need to delete the headless service upfront:

kubectl -n flux delete svc flux-memcached

[squaremo]

There is one caveat with helm upgrade since the ClusterIP field is immutable.

OK -- we'll just need to flag this up in the chart release notes (and give it a minor version bump).

[stefanprodan]

@squaremo I've added a note to the chart changelog with the upgrade instructions.