StatefulSets Made Easier With Istio 1.10
Learn how to easily deploy StatefulSets with Istio 1.10.
Kubernetes StatefulSets are commonly used to manage stateful applications. In addition to managing the deployment and scaling of a set of Pods, StatefulSets provide guarantees about the ordering and uniqueness of those Pods. Common applications used with StatefulSets include ZooKeeper, Cassandra, Elasticsearch, Redis and NiFi.
The Istio community has been making gradual progress towards zero-configuration support for StatefulSets; from automatic mTLS, to eliminating the need to create DestinationRule or ServiceEntry resources, to the most recent pod networking changes in Istio 1.10.
What is unique about using a StatefulSet with a service mesh? The StatefulSet pods are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling. The kind of apps that run in a StatefulSet are often those that need to communicate among their pods, and, as they come from a world of hard-coded IP addresses, may listen on the pod IP only, instead of 0.0.0.0.
ZooKeeper, for example, is configured by default to not listen on all IPs for quorum communication:
quorumListenOnAllIPs=false
Over the last few releases, the Istio community has reported many issues around support for applications running in StatefulSets.
StatefulSets in action, prior to Istio 1.10
In a GKE cluster running Kubernetes 1.19, we have Istio 1.9.5 installed. We enabled automatic sidecar injection in the default namespace, then we installed ZooKeeper using the Helm charts provided by Bitnami, along with the Istio sleep pod for interactive debugging:
$ helm repo add bitnami https://charts.bitnami.com/bitnami
$ helm install my-release bitnami/zookeeper --set replicaCount=3
$ kubectl apply -f https://raw.githubusercontent.com/istio/istio/release-1.21/samples/sleep/sleep.yaml
After a few minutes, all pods come up nicely with sidecar proxies:
$ kubectl get pods,svc
NAME READY STATUS RESTARTS AGE
my-release-zookeeper-0 2/2 Running 0 3h4m
my-release-zookeeper-1 2/2 Running 0 3h4m
my-release-zookeeper-2 2/2 Running 0 3h5m
pod/sleep-8f795f47d-qkgh4 2/2 Running 0 3h8m
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
my-release-zookeeper ClusterIP 10.100.1.113 <none> 2181/TCP,2888/TCP,3888/TCP 3h
my-release-zookeeper-headless ClusterIP None <none> 2181/TCP,2888/TCP,3888/TCP 3h
service/sleep ClusterIP 10.100.9.26 <none> 80/TCP 3h
Are our ZooKeeper services working and is the status Running? Let’s find out! ZooKeeper listens on 3 ports:
- Port 2181 is the TCP port for clients to connect to the ZooKeeper service
- Port 2888 is the TCP port for peers to connect to other peers
- Port 3888 is the dedicated TCP port for leader election
By default, the ZooKeeper installation configures port 2181 to listen on 0.0.0.0 but ports 2888 and 3888 only listen on the pod IP. Let’s check out the network status on each of these ports from one of the ZooKeeper pods:
$ kubectl exec my-release-zookeeper-1 -c istio-proxy -- netstat -na | grep -E '(2181|2888|3888)'
tcp 0 0 0.0.0.0:2181 0.0.0.0:* LISTEN
tcp 0 0 10.96.7.7:3888 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:2181 127.0.0.1:37412 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37486 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37456 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37498 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37384 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37514 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37402 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37434 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37526 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37374 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37442 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:37464 TIME_WAIT
There is nothing ESTABLISHED on port 2888 or 3888. Next, let us get the ZooKeeper server status:
$ kubectl exec my-release-zookeeper-1 -c zookeeper -- /opt/bitnami/zookeeper/bin/zkServer.sh status
/opt/bitnami/java/bin/java
ZooKeeper JMX enabled by default
Using config: /opt/bitnami/zookeeper/bin/../conf/zoo.cfg
Client port found: 2181. Client address: localhost. Client SSL: false.
Error contacting service. It is probably not running.
From the above output, you can see the ZooKeeper service is not functioning properly. Let us check the cluster configuration for one of the ZooKeeper pods:
$ istioctl proxy-config cluster my-release-zookeeper-1 --port 3888 --direction inbound -o json
[
{
"name": "inbound|3888||",
"type": "STATIC",
"connectTimeout": "10s",
"loadAssignment": {
"clusterName": "inbound|3888||",
"endpoints": [
{
"lbEndpoints": [
{
"endpoint": {
"address": {
"socketAddress": {
"address": "127.0.0.1",
"portValue": 3888
}
}
}
}
]
}
]
},
...
What is interesting here is that the inbound on port 3888 has 127.0.0.1 as its endpoint. This is because the Envoy proxy, in versions of Istio prior to 1.10, redirects the inbound traffic to the loopback interface, as described in our blog post about the change.
StatefulSets in action with Istio 1.10
Now, we have upgraded our cluster to Istio 1.10 and configured the default namespace to enable 1.10 sidecar injection. Let’s rolling restart the ZooKeeper StatefulSet to update the pods to use the new version of the sidecar proxy:
$ kubectl rollout restart statefulset my-release-zookeeper
Once the ZooKeeper pods reach the running status, let’s check out the network connections for these 3 ports from any of the ZooKeeper pods:
$ kubectl exec my-release-zookeeper-1 -c istio-proxy -- netstat -na | grep -E '(2181|2888|3888)'
tcp 0 0 0.0.0.0:2181 0.0.0.0:* LISTEN
tcp 0 0 10.96.8.10:2888 0.0.0.0:* LISTEN
tcp 0 0 10.96.8.10:3888 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.6:42571 10.96.8.10:2888 ESTABLISHED
tcp 0 0 10.96.8.10:2888 127.0.0.6:42571 ESTABLISHED
tcp 0 0 127.0.0.6:42655 10.96.8.10:2888 ESTABLISHED
tcp 0 0 10.96.8.10:2888 127.0.0.6:42655 ESTABLISHED
tcp 0 0 10.96.8.10:37876 10.96.6.11:3888 ESTABLISHED
tcp 0 0 10.96.8.10:44872 10.96.7.10:3888 ESTABLISHED
tcp 0 0 10.96.8.10:37878 10.96.6.11:3888 ESTABLISHED
tcp 0 0 10.96.8.10:44870 10.96.7.10:3888 ESTABLISHED
tcp 0 0 127.0.0.1:2181 127.0.0.1:54508 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54616 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54664 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54526 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54532 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54578 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54634 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54588 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54610 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54550 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54560 TIME_WAIT
tcp 0 0 127.0.0.1:2181 127.0.0.1:54644 TIME_WAIT
There are ESTABLISHED connections on both port 2888 and 3888! Next, let us check out the ZooKeeper server status:
$ kubectl exec my-release-zookeeper-1 -c zookeeper -- /opt/bitnami/zookeeper/bin/zkServer.sh status
/opt/bitnami/java/bin/java
ZooKeeper JMX enabled by default
Using config: /opt/bitnami/zookeeper/bin/../conf/zoo.cfg
Client port found: 2181. Client address: localhost. Client SSL: false.
Mode: follower
The ZooKeeper service is now running!
We can connect to each of the ZooKeeper pods from the sleep pod and run the below command to discover the server status of each pod within the StatefulSet. Note that there is no need to create ServiceEntry resources for any of the ZooKeeper pods and we can call these pods directly using their DNS names (e.g. my-release-zookeeper-0.my-release-zookeeper-headless) from the sleep pod.
$ kubectl exec -it deploy/sleep -c sleep -- sh -c 'for x in my-release-zookeeper-0.my-release-zookeeper-headless my-release-zookeeper-1.my-release-zookeeper-headless my-release-zookeeper-2.my-release-zookeeper-headless; do echo $x; echo srvr|nc $x 2181; echo; done'
my-release-zookeeper-0.my-release-zookeeper-headless
Zookeeper version: 3.7.0-e3704b390a6697bfdf4b0bef79e3da7a4f6bac4b, built on 2021-03-17 09:46 UTC
Latency min/avg/max: 1/7.5/20
Received: 3845
Sent: 3844
Connections: 1
Outstanding: 0
Zxid: 0x200000002
Mode: follower
Node count: 6
my-release-zookeeper-1.my-release-zookeeper-headless
Zookeeper version: 3.7.0-e3704b390a6697bfdf4b0bef79e3da7a4f6bac4b, built on 2021-03-17 09:46 UTC
Latency min/avg/max: 0/0.0/0
Received: 3856
Sent: 3855
Connections: 1
Outstanding: 0
Zxid: 0x200000002
Mode: follower
Node count: 6
my-release-zookeeper-2.my-release-zookeeper-headless
Zookeeper version: 3.7.0-e3704b390a6697bfdf4b0bef79e3da7a4f6bac4b, built on 2021-03-17 09:46 UTC
Latency min/avg/max: 0/0.0/0
Received: 3855
Sent: 3854
Connections: 1
Outstanding: 0
Zxid: 0x200000002
Mode: leader
Node count: 6
Proposal sizes last/min/max: 48/48/48
Now our ZooKeeper service is running, let’s use Istio to secure all communication to our regular and headless services. Apply mutual TLS to the default namespace:
$ kubectl apply -n default -f - <<EOF
apiVersion: "security.istio.io/v1beta1"
kind: "PeerAuthentication"
metadata:
name: "default"
spec:
mtls:
mode: STRICT
EOF
Continue sending some traffic from the sleep pod and bring up the Kiali dashboard to visualize the services in the default namespace:
The padlock icons on the traffic flows indicate that the connections are secure.
Wrapping up
With the new networking changes in Istio 1.10, a Kubernetes pod with a sidecar has the same networking behavior as a pod without a sidecar. This change enables stateful applications to function properly in Istio as we have shown you in this post. We believe this is a huge step towards Istio’s goal of providing transparent service mesh and zero-configuration Istio.