How to scale up all OpenShift pods before scaling down old ones - deployment

Question

I have a basic OpenShift deployment configuration:
kind: DeploymentConfig
spec:
replicas: 3
strategy:
type: Rolling
Additionaly I've put:
maxSurge: 3
maxUnavailable: 0%
because I want to scale up all new pods first and after that scale down old pods (so there will be 6 pods running during deploymentm that's why I decided to set up maxSurge).
I want to have all old pods running until all new pods are up but with this set of parameters there is something wrong. During deployment:
all 3 new pods are initialized at once and are trying to start, old pods are running (as expected)
if first new pod started sucessfully then the old one is terminated
if second new pod is ready then another old pod is terminated
I want to terminate all old pods ONLY if all new pods are ready to handle requests, otherwise all the old pods should handle requests.
What did I miss in this confgiuration?

Answer 1

The behavior you document is expected for a deployment rollout (that OpenShift will shut down each old pod as a new pod becomes ready). It will also start routing traffic to the new nodes as they become available, which you say that you don't want either.
A service is pretty much by definition going to route to pods as they are available. And a deployment pretty much handles pods independently, so I don't believe that anything will really give you the behavior you are looking for there either.
If you want a blue green style deployment like you describe, you are essentially going to have deploy the new pods as a separate deployment. Then once the new deployment is completely up, you can change the corresponding service to point at the new pods. Then you can shut down the old deployment.
Service Mesh can help with some of that. So could an operator. Or you could do it manually.

Answer 2

You can combine the rollout strategy with readiness checks with an initial delay to ensure that all the new pods have time to start up before the old ones are all shut down at the same time.
In the case below, the new 3 pods will be spun up (for a total of 6 pods) and then after 60 seconds, the readiness check will occur and the old pods will be shut down. You would just want to adjust your readiness delay to a large enough timeframe to give all of your new pods time to start up.
apiVersion: v1
kind: DeploymentConfig
spec:
replicas: 3
strategy:
rollingParams:
maxSurge: 3
maxUnavailable: 0
type: Rolling
template:
spec:
containers:
- readinessProbe:
httpGet:
path: /actuator/health/readiness
port: 8099
initialDelaySeconds: 60