Rolling restart of pods in deployment

[Keshava Bharadwaj]

Hi,

We have a simple deployment of 3 replicas.

We have a requirement to have a kubernetes cron job, that would need to restart(rolling restart) the pods/containers in the deployment.

Use-case: we use certs in our services in deployment and we need the certificates to be auto renewed before expiry(very short - every 15 days), and hence the cron would restart

the pods before expiry. On a restart, during container startup, it would fetch certificates.

Is this possible to achieve this with existing Deployments construct and API?

From documentation,  -

 A Deployment’s rollout is triggered if and only if the Deployment’s pod template (that is, .spec.template) is changed, for example if the labels or container images of the template are updated. Other updates, such as scaling the Deployment, do not trigger a rollout.

So, i wanted to ask whether - is it possible to have rolling restart of containers declared as part of deployment periodically?

[Tim Hockin]

What I have seen several people do for this is to increment an env
var, or use a timestamp - something trivial that doesn't impact the
app, but forces a restart. Updating an env var can not ever be done
without restart.

On Fri, Dec 15, 2017 at 2:00 AM, Keshava Bharadwaj
<kb.sa...@gmail.com> wrote:
> Hi,
>
> We have a simple deployment of 3 replicas.
> We have a requirement to have a kubernetes cron job, that would need to

> restart(rolling restart) the pods in the deployment.

>
> Use-case: we use certs in our services in deployment and we need the

> certificates to be auto renewed before expiry, and hence the cron would
> restart
> the pods before expiry. On a container startup, it would fetch certificates.
>
> Is this possible with Deployments construct and API?

>
> From documentation, -
>>
>> A Deployment’s rollout is triggered if and only if the Deployment’s pod
>> template (that is, .spec.template) is changed, for example if the labels or
>> container images of the template are updated. Other updates, such as scaling
>> the Deployment, do not trigger a rollout.
>
>
> So, i wanted to ask whether - is it possible to have rolling restart of

> containers periodically?
>
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[Timo Reimann]

I believe you can also update / create an annotation inside the pod spec's metadata section if you fear that an environment variable might collide or just pollute your application's env var space.

More discussions, tips, and related issues regarding the subject of forced restarts can be found in https://github.com/kubernetes/kubernetes/issues/27081.

[Timo Reimann]

Actually, it's the Deployment's pod template (.spec.template) that needs to host the annotation. Always getting confused. https://kubernetes.io/docs/concepts/workloads/controllers/deployment/#updating-a-deployment has it formally defined.

[Keshava Bharadwaj]

Thanks  for the inputs. Using annotations and updating them using patch serves the purpose. 

- Keshava