Recreate Kubernetes deployment with 0 downtime on AWS EKS - amazon-web-services

Question

I have a deployment on Kubernetes (AWS EKS), with several environment variables defined in the deployment .yaml file:
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: myApp
name: myAppName
spec:
replicas: 2
(...)
spec:
containers:
- env:
- name: MY_ENV_VAR
value: "my_value"
image: myDockerImage:prodV1
(...)
If I want to upgrade the pods to another version of the docker image, say prodV2, I can perform a rolling update which replaces the pods from prodV1 to prodV2 with zero downtime.
However, if I add another env variable, say MY_ENV_VAR_2 : "my_value_2" and perform the same rolling update, I don't see the new env var in the container. The only solution I found in order to have both env vars was to manually execute
kubectl delete deployment myAppName
kubectl create deployment -f myDeploymentFile.yaml
As you can see, this is not zero downtime, as deleting the deployment will terminate my pods and introduce a downtime until the new deployment is created and the new pods start.
Is there a way to better do this? Thank you!

Answer 1

Here is an example you might want to test yourself:
Noice I used spec.strategy.type: RollingUpdate.
deployment.yaml:
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: nginx
name: nginx
spec:
replicas: 2
strategy:
type: RollingUpdate
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- image: nginx
name: nginx
env:
- name: MY_ENV_VAR
value: "my_value"
Apply:
➜ ~ kubectl apply -f deployment.yaml
➜ ~ kubectl exec -it nginx-<hash> env | grep MY_ENV_VAR
MY_ENV_VAR=my_value
Notice the env is as set in yaml
Now we edit the env in deployment.yaml:
deployment.yaml:
apiVersion: apps/v1
kind: Deployment
metadata:
labels:
app: nginx
name: nginx
spec:
replicas: 2
strategy:
type: RollingUpdate
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- image: nginx
name: nginx
env:
- name: MY_ENV_VAR
value: "my_new_value"
apply and wait for it to update:
➜ ~ kubectl apply -f deployment.yaml
➜ ~ kubectl get po --watch
# after it updated use Ctrl+C to stop the watch and run:
➜ ~ kubectl exec -it nginx-<new_hash> env | grep MY_ENV_VAR
MY_ENV_VAR=my_new_value
As you should see, the env changed. That is pretty much it.