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Running KUDO Kafka in production

Checklist

  • Verify the storage class features
  • Broker configuration
  • Run the KUDO Kafka with tuned parameters

This document optimizes for data durability over performance.

Storage Class features

Verify if there is a storage class installed in the Kubernetes cluster. In this example we will use the aws-ebs-csi-driver as the storage class reference.

$ kubectl get sc
NAME                             PROVISIONER       AGE
awsebscsiprovisioner (default)   ebs.csi.aws.com   2d

Volume Expansion

Verify if the storage class has the option AllowVolumeExpansion and is set to true.

$ kubectl describe sc awsebscsiprovisioner
Name:                  awsebscsiprovisioner
IsDefaultClass:        Yes
Annotations:           kubernetes.io/description=AWS EBS CSI provisioner StorageClass,storageclass.kubernetes.io/is-default-class=true
Provisioner:           ebs.csi.aws.com
Parameters:            type=gp2
AllowVolumeExpansion:  true
MountOptions:          <none>
ReclaimPolicy:         Delete
VolumeBindingMode:     WaitForFirstConsumer
Events:                <none>

⚠️ In case AllowVolumeExpansion is unset or false, make sure to provision enough disk when bootstrapping the KUDO Kafka cluster. The disk size can be configured using the DISK_SIZE parameter. By default, DISK_SIZE is set to 5Gi and is not ideal for production usage. Users should Increase disk size by as much as they deem necessary for reliable stability.

ReclaimPolicy

Verify the storage class has the option ReclaimPolicy and is set to Retain.

To read more about the ReclaimPolicy read the official Kubernetes docs on Changing the Reclaim Policy

> PersistentVolumes can have various reclaim policies, including “Retain”, “Recycle”, and “Delete”. For dynamically provisioned PersistentVolumes, the default reclaim policy is “Delete”. This means that a dynamically provisioned volume is automatically deleted when a user deletes the corresponding PersistentVolumeClaim. This automatic behavior might be inappropriate if the volume contains precious data. In that case, it is more appropriate to use the “Retain” policy. With the “Retain” policy, if a user deletes a PersistentVolumeClaim, the corresponding PersistentVolume is not be deleted. Instead, it is moved to the Released phase, where all of its data can be manually recovered.

If the StorageClass is to be shared between many users, a common practice is to leave the default ReclaimPolicy as Delete and set ReclaimPolicy: Retain in the PersistentVolume once the cluster is up and running.

Let's see an example of a 3-broker KUDO Kafka cluster's PersistentVolumes where the StorageClass default ReclaimPolicy is Delete

$ kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                                                              STORAGECLASS           REASON   AGE
pvc-6a9e69f4-b807-440f-b190-357c109e8ad9   5Gi        RWO            Delete           Bound    default/kafka-datadir-kafka-kafka-0                                awsebscsiprovisioner            18h
pvc-8602a698-14a0-4c3d-85e6-67eb6da80a5d   5Gi        RWO            Delete           Bound    default/kafka-datadir-kafka-kafka-2                                awsebscsiprovisioner            18h
pvc-de527673-8bee-4e38-9e6d-399ec07c2728   5Gi        RWO            Delete           Bound    default/kafka-datadir-kafka-kafka-1                                awsebscsiprovisioner            18h

We can patch the PersistentVolumes to use the ReclaimPolicy of Retain

$ kubectl patch pv pvc-6a9e69f4-b807-440f-b190-357c109e8ad9 -p '{"spec":{"persistentVolumeReclaimPolicy":"Retain"}}'
$ kubectl patch pv pvc-8602a698-14a0-4c3d-85e6-67eb6da80a5d -p '{"spec":{"persistentVolumeReclaimPolicy":"Retain"}}'
$ kubectl patch pv pvc-de527673-8bee-4e38-9e6d-399ec07c2728 -p '{"spec":{"persistentVolumeReclaimPolicy":"Retain"}}'

persistentvolume/pvc-6a9e69f4-b807-440f-b190-357c109e8ad9 patched
persistentvolume/pvc-8602a698-14a0-4c3d-85e6-67eb6da80a5d patched
persistentvolume/pvc-de527673-8bee-4e38-9e6d-399ec07c2728 patched

Verify the PersistentVolumes ReclaimPolicy has been changed for all brokers:

$ kubectl get pv
pvc-6a9e69f4-b807-440f-b190-357c109e8ad9   5Gi        RWO            Retain           Bound    default/kafka-datadir-kafka-kafka-0                                awsebscsiprovisioner            18h
pvc-8602a698-14a0-4c3d-85e6-67eb6da80a5d   5Gi        RWO            Retain           Bound    default/kafka-datadir-kafka-kafka-2                                awsebscsiprovisioner            18h
pvc-de527673-8bee-4e38-9e6d-399ec07c2728   5Gi        RWO            Retain           Bound    default/kafka-datadir-kafka-kafka-1                                awsebscsiprovisioner            18h

Broker configuration

Replication Factor

Change the default replication factor from the default 1 to 3.

DEFAULT_REPLICATION_FACTOR=3

Minimum Insync Replicas

MIN_INSYNC_REPLICAS is the minimum number of replicas that must acknowledge a write for the write to be considered successful. To enforce greater durability guarantees, Kafka users should use MIN_INSYNC_REPLICAS in conjunction with producer acks.

To guarantee message durability, a recommended practice is to create a topic with a replication factor of 3, set MIN_INSYNC_REPLICAS to 2, and produce messages with acks of all.

MIN_INSYNC_REPLICAS=2

Number of partitions

The number of partitions should be higher than 1 for reliability reasons. By default, this option is set to 3.

More partitions lead to higher throughput performance but affect latency and availability. In KUDO Kafka we can balance this trade-off of throughput vs. availability by configuring the default partition number.

NUM_PARTITIONS=3

Graceful rolling restarts

By default, KUDO Kafka sets CONTROLLED_SHUTDOWN_ENABLE to true. Which means whenever the pods are restarted the broker does a controlled shutdown. That process includes a log flush. During these controlled shutdown and bootstrap periods Apache Kafka's LogManager uses a Threadpool. To ensure a faster flush during shutdown, and faster recovery during bootstrap, we can configure the threads in the LogManager Threadpool using the property num.recovery.threads.per.data.dir. Which can be increased from the default value of 1 thread.

NUM_RECOVERY_THREADS_PER_DATA_DIR=3

Network Threads

If users expect the Kafka cluster to receive a high number of incoming requests, then users may need to increase the the number of network threads from its default value of of 3. This is important for clusters where a lot of different producers are connecting and writing messages.

NUM_NETWORK_THREADS=10

Max Queued Requests

The number of queued requests allowed before blocking the network threads. The default 500 is sufficient for normal workloads. In case you have sharp peaks of workload where, for a short time, much load is thrown towards the Kafka cluster, you might need to tweak this value accordingly to not block any incoming requests during those peaks.

QUEUED_MAX_REQUESTS=<USER_CUSTOM_VALUE>

Background threads

The threads that are doing background jobs for the Kafka cluster, including compaction of log files, triggering leader election, and leader rebalance jobs. The default number of threads of 10 should be sufficient.

BACKGROUND_THREADS=10

Run the KUDO Kafka with tuned parameters

$ kubectl kudo install kafka \
    --instance=kafka-instance --namespace=kudo-kafka -p ZOOKEEPER_URI=$ZOOKEEPER_URI \
    -p BROKER_CPUS=2000m \
    -p BROKER_COUNT=5 \
    -p BROKER_MEM=4096m \
    -p DISK_SIZE=100Gi \
    -p NUM_RECOVERY_THREADS_PER_DATA_DIR=3 \
    -p DEFAULT_REPLICATION_FACTOR=3 \
    -p MIN_INSYNC_REPLICAS=2 \
    -p NUM_NETWORK_THREADS=10 \
    -p NUM_PARTITIONS=3 \
    -p QUEUED_MAX_REQUESTS=1000