Mention rolling update strategy is not appropriate for Crate major version upgrade

[c0c0n3]

Our Crate chart instantiates a K8s statefulset with a rolling update strategy. With this strategy in place, on detecting a new Crate image, K8s will delete and then recreate each pod with the new image, one at a time. So while upgrading, most of the time you'll be in a situation where some of the pods are running the old image whereas some others are on the new. Crate docs say this is fine only when upgrading to a new patch version whereas to upgrade to a new minor or major version you should first shut down the entire cluster, then upgrade images, and finally bring the new cluster live. This latter procedure isn't compatible with K8s rolling update strategy so we should warn users about it. For example we could mention it in the chart README.

[amotl]

Dear @c0c0n3,

by following up on our conversation at orchestracities/ngsi-timeseries-api#384 (comment) ff. - FWIW, I would also like to reference crate/crate-operator#127 here, where I asked back about whether topics mentioned here might be implemented through the CrateDB Kubernetes Operator or not.

With kind regards,
Andreas.

[c0c0n3]

Dear @amotl, thank you sooo much for being so proactive. It really helps us alot. I added my comments to crate/crate-operator#127. Many thanks!!

[c0c0n3]

@chicco785 the bottom line for now is:

• K8s rolling upgrade isn't the proper way to upgrade to a new major version number, but should work fine between minor versions
• There's a very nice tool the Crate guys have been working on for Crate/K8s deployments: https://github.com/crate/crate-operator
• There are plans for the Crate Operator to support Crate major version upgrades: Support CrateDB major upgrade with full cluster restarts crate/crate-operator#128

We should keep an eye on the above issue, since Crate Operator looks like a very nice option for our prod deployments.

[chicco785]

@chicco785 the bottom line for now is:

• K8s rolling upgrade isn't the proper way to upgrade to a new major version number, but should work fine between minor versions

yep, I think this was clear given current experience

• There's a very nice tool the Crate guys have been working on for Crate/K8s deployments: https://github.com/crate/crate-operator

that's very interesting, the issue for us is that we would need to be able to reuse existing pvc, or it will be a pain to migrate data. i suppose it works quite well also with fluxctl

• There are plans for the Crate Operator to support Crate major version upgrades: crate/crate-operator#128

We should keep an eye on the above issue, since Crate Operator looks like a very nice option for our prod deployments.

[c0c0n3]

would need to be able to reuse existing pvc

I think the Crate Operator will leave it be, if I understand the way it works but I could be wrong :-)