Gateway Termination
In today's chaos day, we wanted to experiment with the gateway and resiliency of workers.
We have seen in recent weeks some issues within our benchmarks when gateways have been restarted, see zeebe#11975.
We did a similar experiment in the past, today we want to focus on self-managed (benchmarks with our helm charts). Ideally, we can automate this as well soon.
Today Nicolas joined me on the chaos day 🎉
TL;DR; We were able to show that the workers (clients) can reconnect after a gateway is shutdown ✅ Furthermore, we have discovered a potential performance issue on lower load, which impacts process execution latency (zeebe#12311).
Chaos Experiment
We will use our Zeebe benchmark helm charts to set up the test cluster, and our helper scripts here.
Setup:
We will run with the default benchmark configuration, which means:
- three brokers
- three partitions
- replication count three
- two gateways
We will run the benchmark with a low load, 10 process instances per second created and completed. For that, we deploy one starter and worker. This reduces the blast radius and allows us to observe more easily how the workers behave when a gateway is restarted.
During the experiment, we will use our grafana dashboard to observe to which gateway the worker will connect and which gateway we need to stop/restart.
LAST DEPLOYED: Thu Apr 6 10:21:27 2023
NAMESPACE: zell-chaos
STATUS: deployed
REVISION: 1
NOTES:
# Zeebe Benchmark
Installed Zeebe cluster with:
* 3 Brokers
* 2 Gateways
The benchmark is running with:
* Starter replicas=1
* Worker replicas=1
* Publisher replicas=0
* Timer replicas=0
Expected
When we terminate a gateway to which the worker has connected, we expect that the worker connects to the different replica and starts completing jobs again.
The performance drop is expected to be not significant, or at least should recover fast.
Actual
We will run the experiment in two ways, first via terminating the gateway (using zbchaos) and later via scaling down the gateway deployment to one replica.
We want to verify whether this makes any difference, since terminating will cause Kubernetes to recreate immediately the pod.
Termination
Before we start the experiment we check our current deployed state:
$ kgpo
NAME READY STATUS RESTARTS AGE
camunda-platform-curator-28012860-zk72q 0/1 Completed 0 7m24s
elasticsearch-master-0 1/1 Running 0 45m
elasticsearch-master-1 1/1 Running 0 45m
elasticsearch-master-2 1/1 Running 0 45m
leader-balancer-28012860-7cwmd 0/1 Completed 0 7m25s
starter-cb69c447f-l2zbh 1/1 Running 0 45m
worker-cb7f7c469-qvqqv 1/1 Running 0 45m
zell-chaos-zeebe-0 1/1 Running 0 45m
zell-chaos-zeebe-1 1/1 Running 0 45m
zell-chaos-zeebe-2 1/1 Running 0 45m
zell-chaos-zeebe-gateway-7bbdf9fd58-vs28f 1/1 Running 0 45m
zell-chaos-zeebe-gateway-7bbdf9fd58-xc6d9 1/1 Running 0 45m
Via our Grafana dashboard (and the gRPC metrics) we are able to track to which gateway the worker connects to:
It is zell-chaos-zeebe-gateway-7bbdf9fd58-vs28f.
Via zbchaos we can easily terminate the gateway (it will always take the first in the pod list).
$ zbchaos terminate gateway
{1 LEADER -1 10 msg false 1 LEADER -1 2 LEADER -1 1680772377704 false false true false false 30 false -1 benchmark 30 }
Terminated zell-chaos-zeebe-gateway-7bbdf9fd58-vs28f
After terminating we can see that a new gateway pod has started.
$ kgpo
NAME READY STATUS RESTARTS AGE
camunda-platform-curator-28012860-zk72q 0/1 Completed 0 13m
elasticsearch-master-0 1/1 Running 0 52m
elasticsearch-master-1 1/1 Running 0 52m
elasticsearch-master-2 1/1 Running 0 52m
leader-balancer-28012860-7cwmd 0/1 Completed 0 13m
starter-cb69c447f-l2zbh 1/1 Running 0 52m
worker-cb7f7c469-qvqqv 1/1 Running 0 52m
zell-chaos-zeebe-0 1/1 Running 0 52m
zell-chaos-zeebe-1 1/1 Running 0 52m
zell-chaos-zeebe-2 1/1 Running 0 52m
zell-chaos-zeebe-gateway-7bbdf9fd58-pkj48 1/1 Running 0 33s
zell-chaos-zeebe-gateway-7bbdf9fd58-xc6d9 1/1 Running 0 52m
In the metrics, we can see that due to the restart, the throughput slightly dropped, but recovered pretty fast. The worker was able to connect to the different gateway. ✅
Note
In the panel
Pod Restartson the top right, we don't see any restarts and that is something we should always be aware of that the metrics are just samples of data. If a pod, like a gateway, restarts fast enough and the metric collect interval is higher (per default we have ~30 s (?)) then you might not see a change.
Scale down
As described earlier we wanted to verify whether it makes a difference if we scale down the replica instead of terminating/restarting it, which causes restarting a new pod (which might get the same IP).
For scaling down Nicolas found this annotation: controller.kubernetes.io/pod-deletion-cost
This means we edit one pod and gave the following annotation:
annotations:
controller.kubernetes.io/pod-deletion-cost: "-1"
We have similarly chosen the pod as we have seen above, based on the gRPC metrics.
Checking the running pods and editing the correct gateway:
[cqjawa 2023-04-06-gateway-termination/ cluster: zeebe-cluster ns:zell-chaos]$ kgpo
NAME READY STATUS RESTARTS AGE
camunda-platform-curator-28012875-tntdv 0/1 Completed 0 6m26s
elasticsearch-master-0 1/1 Running 0 59m
elasticsearch-master-1 1/1 Running 0 59m
elasticsearch-master-2 1/1 Running 0 59m
leader-balancer-28012875-sctwq 0/1 Completed 0 6m26s
starter-cb69c447f-l2zbh 1/1 Running 0 59m
worker-cb7f7c469-qvqqv 1/1 Running 0 59m
zell-chaos-zeebe-0 1/1 Running 0 59m
zell-chaos-zeebe-1 1/1 Running 0 59m
zell-chaos-zeebe-2 1/1 Running 0 59m
zell-chaos-zeebe-gateway-7bbdf9fd58-pkj48 1/1 Running 0 8m29s
zell-chaos-zeebe-gateway-7bbdf9fd58-xc6d9 1/1 Running 0 59m
When I did the following I was wondering why it didn't scale down the deployment, one pod was recreated.
[cqjawa 2023-04-06-gateway-termination/ cluster: zeebe-cluster ns:zell-chaos]$ k scale replicaset zell-chaos-zeebe-gateway-7bbdf9fd58 --replicas=1
Warning: spec.template.spec.containers[0].env[16].name: duplicate name "ZEEBE_LOG_LEVEL"
replicaset.apps/zell-chaos-zeebe-gateway-7bbdf9fd58 scaled
[cqjawa 2023-04-06-gateway-termination/ cluster: zeebe-cluster ns:zell-chaos]$ kgpo
NAME READY STATUS RESTARTS AGE
camunda-platform-curator-28012875-tntdv 0/1 Completed 0 6m53s
elasticsearch-master-0 1/1 Running 0 60m
elasticsearch-master-1 1/1 Running 0 60m
elasticsearch-master-2 1/1 Running 0 60m
leader-balancer-28012875-sctwq 0/1 Completed 0 6m53s
starter-cb69c447f-l2zbh 1/1 Running 0 60m
worker-cb7f7c469-qvqqv 1/1 Running 0 60m
zell-chaos-zeebe-0 1/1 Running 0 60m
zell-chaos-zeebe-1 1/1 Running 0 60m
zell-chaos-zeebe-2 1/1 Running 0 60m
zell-chaos-zeebe-gateway-7bbdf9fd58-2v6gs 0/1 PodInitializing 0 7s
zell-chaos-zeebe-gateway-7bbdf9fd58-pkj48 1/1 Running 0 8m56s
Note:
During the experiment I learned that when you have deployed a deployment, you need to scale down the deployment, not the ReplicaSet. Otherwise your Kubernetes deployment controller will recreate the ReplicaSet in the next reconcile loop, which means you will have again the same replicas as defined in the deployment.
So correct is to scale down the deployment (!), if you ever wonder.
[cqjawa 2023-04-06-gateway-termination/ cluster: zeebe-cluster ns:zell-chaos]$ k edit pod zell-chaos-zeebe-gateway-7bbdf9fd58-pkj48
pod/zell-chaos-zeebe-gateway-7bbdf9fd58-pkj48 edited
[cqjawa 2023-04-06-gateway-termination/ cluster: zeebe-cluster ns:zell-chaos]$ kgpo
NAME READY STATUS RESTARTS AGE
camunda-platform-curator-28012875-tntdv 0/1 Completed 0 10m
elasticsearch-master-0 1/1 Running 0 63m
elasticsearch-master-1 1/1 Running 0 63m
elasticsearch-master-2 1/1 Running 0 63m
leader-balancer-28012875-sctwq 0/1 Completed 0 10m
starter-cb69c447f-l2zbh 1/1 Running 0 63m
worker-cb7f7c469-qvqqv 1/1 Running 0 63m
zell-chaos-zeebe-0 1/1 Running 0 63m
zell-chaos-zeebe-1 1/1 Running 0 63m
zell-chaos-zeebe-2 1/1 Running 0 63m
zell-chaos-zeebe-gateway-7bbdf9fd58-2v6gs 1/1 Running 0 3m40s
zell-chaos-zeebe-gateway-7bbdf9fd58-pkj48 1/1 Running 0 12m
[cqjawa 2023-04-06-gateway-termination/ cluster: zeebe-cluster ns:zell-chaos]$ k scale deployment zell-chaos-zeebe-gateway --replicas=1
Warning: spec.template.spec.containers[0].env[16].name: duplicate name "ZEEBE_LOG_LEVEL"
deployment.apps/zell-chaos-zeebe-gateway scaled
[cqjawa 2023-04-06-gateway-termination/ cluster: zeebe-cluster ns:zell-chaos]$ kgpo
NAME READY STATUS RESTARTS AGE
camunda-platform-curator-28012875-tntdv 0/1 Completed 0 10m
elasticsearch-master-0 1/1 Running 0 64m
elasticsearch-master-1 1/1 Running 0 64m
elasticsearch-master-2 1/1 Running 0 64m
leader-balancer-28012875-sctwq 0/1 Completed 0 10m
starter-cb69c447f-l2zbh 1/1 Running 0 64m
worker-cb7f7c469-qvqqv 1/1 Running 0 64m
zell-chaos-zeebe-0 1/1 Running 0 64m
zell-chaos-zeebe-1 1/1 Running 0 64m
zell-chaos-zeebe-2 1/1 Running 0 64m
zell-chaos-zeebe-gateway-7bbdf9fd58-2v6gs 1/1 Running 0 4m
With that, we have only one gateway pod left, and all traffic goes to that gateway. Based on the metrics we can see that the workers recovered everytime when we restarted/terminated or scaled down.
The experiment itself succeeded 💪 :white_check_marks:
Found Bugs
Zbchaos print verbose logs
I realized that we still have the issue with zbchaos which is printing verbose logs:
$ zbchaos terminate gateway
{1 LEADER -1 10 msg false 1 LEADER -1 2 LEADER -1 1680772377704 false false true false false 30 false -1 benchmark 30 }
Terminated zell-chaos-zeebe-gateway-7bbdf9fd58-vs28f
Segment creation impact
During checking the metrics together with Nicolas, we realized that even on low load (10 PI/s) we have high spikes in our processing execution latency.
The spikes are going up to 1-1.5 seconds, while the avg is at 0.06s. This happens every 6 minutes.
We can see that the commit latency is as well at the same time high, which might be an issue because of the high IO.
We first expected that to be related to snapshotting, but snapshots happen much more often.
Interestingly is that it seems to be related to our segment creation (again), even if we have async segment creation in our journal built recently. We need to investigate this further within zeebe#12311.
