No-downtime NGINX Kubernetes deployments

nginx-no-downtime.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-no-downtime
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx-no-downtime
  strategy:
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 0
    type: RollingUpdate
  template:
    metadata:
      labels:
        app: nginx-no-downtime
    spec:
      terminationGracePeriodSeconds: 30
      containers:
      - name: nginx-no-downtime
        image: nginx:latest
        # By default, Kubernetes sends a SIGTERM signal to a container when it's safe to terminate it,
        # e.g. when another instance of this deployment becomes available during a rollout.
        # NGINX will interpret this signal as a "fast shutdown", i.e. it will not gracefully shut down
        # and will not wait until until any existing connections have finished. 
        # This will lead to dropped connections and "5xx" response codes.
        # @see https://ubuntu.com/blog/avoiding-dropped-connections-in-nginx-containers-with-stopsignal-sigquit
        #
        # It could be assumed that a new instance of the Nginx deployment requires startupProbes or readinessProbes
        # to determine if the new instance can receive traffic, however that assumption is incorrect.
        # Instead, the issue is related to the existing instance of the Nginx deployment pre-maturely terminating
        # without waiting for all connections to finish.
        #
        # We want NGINX to gracefully terminate and wait until any existing connections finish.
        # To achieve this, we plug in to the "preStop" Kubernetes lifecycle event, which allows us to
        # execute a command before Kubernetes sends the SIGTERM signal.
        # For this event stage, we shut down NGINX gracefully ourselves. This will wait for up to
        # the value of terminationGracePeriodSeconds (default = 30 seconds) and then continue
        # with the container termination. In our testing, this has lead to no dropped connections
        # during load testing & triggering a deployment event for a deployment with 1 replica.
        # @see https://nginx.org/en/docs/control.html
        # @see https://medium.com/inside-personio/graceful-shutdown-of-fpm-and-nginx-in-kubernetes-f362369dff22
        lifecycle:
          preStop:
            exec:
              command:
              - /bin/sh
              - -c
              - kill -s QUIT $(cat /var/run/nginx.pid)