docker build -t <dockerimage-name> \ --build-arg SLACK_WEBHOOK_URL_ARG=${SLACK_WEBHOOK_URL} \ --build-arg CLUSTER_NAMESPACE_ARG=${CLUSTER_NAMESPACE}

After building the image you can run this in your local, however it's not recommended to include your secret like the webhook into your Dockerimage directly.

• Build

docker build -t <dockerimage-name> 

• Push Dockerimage
• Create a Secret

kubectl -n <NAMESPACE> create secret generic app-secret --from-literal=slackwebhook='<SLACK_WEBHOOK>' 

• Change the fields of $namespace, $clusterNamespace, and $imageName.
• You can use kubectl apply -f k8s --recursive