Manage replicas count for deployment using Kubernetes API

the easiest way is to retrieve the actual data first with:

GET /apis/extensions/v1beta1/namespaces/{namespace}/deployments/{name}/scale

This will give you an yaml or json object which you can modify and send back with the PUT request.

---

With curl the roundtrip look like this:

API_URL="http://kubernetes:8080/apis/extensions/v1beta1/namespaces/{namespace}/deployments/{name}/scale"
curl  -H 'Accept: application/json' $API_URL > scale.json
# edit scale.json
curl -X PUT [email protected] -H 'Content-Type: application/json' $API_URL

---

Alternatively you could just use a PATCH call:

PAYLOAD='[{"op":"replace","path":"/spec/replicas","value":"3"}]'
curl -X PATCH -d$PAYLOAD -H 'Content-Type: application/json-patch+json' $API_URL

The previous solution didn't work for me on kubernetes 1.14. I had to use a different API endpoint. Here's the full example:

#!/bin/sh

set -e

NUMBER_OF_REPLICAS="$1"
CURRENT_NAMESPACE="$2"
DEPLOYMENT_NAME="$3"

KUBE_TOKEN=$(cat /var/run/secrets/kubernetes.io/serviceaccount/token)
KUBE_CACRT_PATH="/var/run/secrets/kubernetes.io/serviceaccount/ca.crt"

PAYLOAD="{\"spec\":{\"replicas\":$NUMBER_OF_REPLICAS}}"

curl --cacert $KUBE_CACRT_PATH \
     -X PATCH \
     -H "Content-Type: application/strategic-merge-patch+json" \
     -H "Authorization: Bearer $KUBE_TOKEN" \
     --data "$PAYLOAD" \
     https://$KUBERNETES_SERVICE_HOST/apis/apps/v1/namespaces/$CURRENT_NAMESPACE/deployments/$DEPLOYMENT_NAME

Note that the $KUBERNETES_SERVICE_HOST is automatically set by kubernetes inside the pods.