feat: Add kafka rack aware injection on docker-server (#17541)

Add kafka rack aware injection on docker-server

Currently we only inject this in plugin-server (aka reading from kafka)

Let's add it as well to docker-server (aka capture/writing to kafka)

bin/docker-server

@@ -11,6 +11,13 @@ trap 'rm -rf "$PROMETHEUS_MULTIPROC_DIR"' EXIT
 export PROMETHEUS_METRICS_EXPORT_PORT=8001
 export STATSD_PORT=${STATSD_PORT:-8125}
 
+if [[ -n $INJECT_EC2_CLIENT_RACK ]]; then
+  # To avoid cross-AZ Kafka traffic, set KAFKA_CLIENT_RACK from the EC2 metadata endpoint.
+  # TODO: switch to the downwards API when https://github.com/kubernetes/kubernetes/issues/40610 is released
+  TOKEN=$(curl --max-time 0.1 -X PUT "http://169.254.169.254/latest/api/token" -H "X-aws-ec2-metadata-token-ttl-seconds: 21600")
+  export KAFKA_CLIENT_RACK=$(curl --max-time 0.1 -H "X-aws-ec2-metadata-token: $TOKEN" -v http://169.254.169.254/latest/meta-data/placement/availability-zone-id)
+fi
+
 exec gunicorn posthog.wsgi \
     --config gunicorn.config.py \
     --bind 0.0.0.0:8000 \