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Chapter 4. Sharding clusters across Argo CD Application Controller replicas
You can shard clusters across multiple Argo CD Application Controller replicas if the controller is managing too many clusters and uses too much memory.
4.1. Enabling the round-robin sharding algorithm
The round-robin
sharding algorithm is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.
For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.
By default, the Argo CD Application Controller uses the non-uniform legacy
hash-based sharding algorithm to assign clusters to shards. This can result in uneven cluster distribution. You can enable the round-robin
sharding algorithm to achieve more equal cluster distribution across all shards.
Using the round-robin
sharding algorithm in Red Hat OpenShift GitOps provides the following benefits:
- Ensure more balanced workload distribution
- Prevent shards from being overloaded or underutilized
- Optimize the efficiency of computing resources
- Reduce the risk of bottlenecks
- Improve overall performance and reliability of the Argo CD system
The introduction of alternative sharding algorithms allows for further customization based on specific use cases. You can select the algorithm that best aligns with your deployment needs, which results in greater flexibility and adaptability in diverse operational scenarios.
To leverage the benefits of alternative sharding algorithms in GitOps, it is crucial to enable sharding during deployment.
4.1.1. Enabling the round-robin sharding algorithm in the web console
You can enable the round-robin
sharding algorithm by using the OpenShift Container Platform web console.
Prerequisites
- You have installed the Red Hat OpenShift GitOps Operator on your OpenShift Container Platform cluster.
- You have access to the OpenShift Container Platform web console.
-
You have access to the cluster with
cluster-admin
privileges.
Procedure
-
In the Administrator perspective of the web console, go to Operators
Installed Operators. - Click Red Hat OpenShift GitOps from the installed operators and go to the Argo CD tab.
-
Click the Argo CD instance where you want to enable the
round-robin
sharding algorithm, for example,openshift-gitops
. Click the YAML tab and edit the YAML file as shown in the following example:
Example Argo CD instance with round-robin sharding algorithm enabled
apiVersion: argoproj.io/v1beta1 kind: ArgoCD metadata: name: openshift-gitops namespace: openshift-gitops spec: controller: sharding: enabled: true 1 replicas: 3 2 env: 3 - name: ARGOCD_CONTROLLER_SHARDING_ALGORITHM value: round-robin logLevel: debug 4
Click Save.
A success notification alert,
openshift-gitops has been updated to version <version>
, appears.NoteIf you edit the default
openshift-gitops
instance, the Managed resource dialog box is displayed. Click Save again to confirm the changes.Verify that the sharding is enabled with
round-robin
as the sharding algorithm by performing the following steps:-
Go to Workloads
StatefulSets. - Select the namespace where you installed the Argo CD instance from the Project drop-down list.
- Click <instance_name>-application-controller, for example, openshift-gitops-application-controller, and go to the Pods tab.
- Observe the number of created application controller pods. It should correspond with the number of set replicas.
Click on the controller pod you want to examine and go to the Logs tab to view the pod logs.
Example controller pod logs snippet
time="2023-12-13T09:05:34Z" level=info msg="ArgoCD Application Controller is starting" built="2023-12-01T19:21:49Z" commit=a3vd5c3df52943a6fff6c0rg181fth3248976299 namespace=openshift-gitops version=v2.9.2+c5ea5c4 time="2023-12-13T09:05:34Z" level=info msg="Processing clusters from shard 1" time="2023-12-13T09:05:34Z" level=info msg="Using filter function: round-robin" 1 time="2023-12-13T09:05:34Z" level=info msg="Using filter function: round-robin" time="2023-12-13T09:05:34Z" level=info msg="appResyncPeriod=3m0s, appHardResyncPeriod=0s"
- 1
- Look for the
"Using filter function: round-robin"
message.
In the log Search field, search for
processed by shard
to verify that the cluster distribution across shards is even, as shown in the following example.ImportantEnsure that you set the log level to
debug
to observe these logs.Example controller pod logs snippet
time="2023-12-13T09:05:34Z" level=debug msg="ClustersList has 3 items" time="2023-12-13T09:05:34Z" level=debug msg="Adding cluster with id= and name=in-cluster to cluster's map" time="2023-12-13T09:05:34Z" level=debug msg="Adding cluster with id=068d8b26-6rhi-4w23-jrf6-wjjfyw833n23 and name=in-cluster2 to cluster's map" time="2023-12-13T09:05:34Z" level=debug msg="Adding cluster with id=836d8b53-96k4-f68r-8wq0-sh72j22kl90w and name=in-cluster3 to cluster's map" time="2023-12-13T09:05:34Z" level=debug msg="Cluster with id= will be processed by shard 0" 1 time="2023-12-13T09:05:34Z" level=debug msg="Cluster with id=068d8b26-6rhi-4w23-jrf6-wjjfyw833n23 will be processed by shard 1" 2 time="2023-12-13T09:05:34Z" level=debug msg="Cluster with id=836d8b53-96k4-f68r-8wq0-sh72j22kl90w will be processed by shard 2" 3
NoteIf the number of clusters "C" is a multiple of the number of shard replicas "R", then each shard must have the same number of assigned clusters "N", which is equal to "C" divided by "R". The previous example shows 3 clusters and 3 replicas; therefore, each shard has 1 cluster assigned.
-
Go to Workloads
4.1.2. Enabling the round-robin sharding algorithm by using the CLI
You can enable the round-robin
sharding algorithm by using the command-line interface.
Prerequisites
- You have installed the Red Hat OpenShift GitOps Operator on your OpenShift Container Platform cluster.
-
You have access to the cluster with
cluster-admin
privileges.
Procedure
Enable sharding and set the number of replicas to the wanted value by running the following command:
$ oc patch argocd <argocd_instance> -n <namespace> --patch='{"spec":{"controller":{"sharding":{"enabled":true,"replicas":<value>}}}}' --type=merge
Example output
argocd.argoproj.io/<argocd_instance> patched
Configure the sharding algorithm to
round-robin
by running the following command:$ oc patch argocd <argocd_instance> -n <namespace> --patch='{"spec":{"controller":{"env":[{"name":"ARGOCD_CONTROLLER_SHARDING_ALGORITHM","value":"round-robin"}]}}}' --type=merge
Example output
argocd.argoproj.io/<argocd_instance> patched
Verify that the number of Argo CD Application Controller pods corresponds with the number of set replicas by running the following command:
$ oc get pods -l app.kubernetes.io/name=<argocd_instance>-application-controller -n <namespace>
Example output
NAME READY STATUS RESTARTS AGE <argocd_instance>-application-controller-0 1/1 Running 0 11s <argocd_instance>-application-controller-1 1/1 Running 0 32s <argocd_instance>-application-controller-2 1/1 Running 0 22s
Verify that the sharding is enabled with
round-robin
as the sharding algorithm by running the following command:$ oc logs <argocd_application_controller_pod> -n <namespace>
Example output snippet
time="2023-12-13T09:05:34Z" level=info msg="ArgoCD Application Controller is starting" built="2023-12-01T19:21:49Z" commit=a3vd5c3df52943a6fff6c0rg181fth3248976299 namespace=<namespace> version=v2.9.2+c5ea5c4 time="2023-12-13T09:05:34Z" level=info msg="Processing clusters from shard 1" time="2023-12-13T09:05:34Z" level=info msg="Using filter function: round-robin" 1 time="2023-12-13T09:05:34Z" level=info msg="Using filter function: round-robin" time="2023-12-13T09:05:34Z" level=info msg="appResyncPeriod=3m0s, appHardResyncPeriod=0s"
- 1
- Look for the
"Using filter function: round-robin"
message.
Verify that the cluster distribution across shards is even by performing the following steps:
Set the log level to
debug
by running the following command:$ oc patch argocd <argocd_instance> -n <namespace> --patch='{"spec":{"controller":{"logLevel":"debug"}}}' --type=merge
Example output
argocd.argoproj.io/<argocd_instance> patched
View the logs and search for
processed by shard
to observe to which shard each cluster is attached by running the following command:$ oc logs <argocd_application_controller_pod> -n <namespace> | grep "processed by shard"
Example output snippet
time="2023-12-13T09:05:34Z" level=debug msg="Cluster with id= will be processed by shard 0" 1 time="2023-12-13T09:05:34Z" level=debug msg="Cluster with id=068d8b26-6rhi-4w23-jrf6-wjjfyw833n23 will be processed by shard 1" 2 time="2023-12-13T09:05:34Z" level=debug msg="Cluster with id=836d8b53-96k4-f68r-8wq0-sh72j22kl90w will be processed by shard 2" 3
NoteIf the number of clusters "C" is a multiple of the number of shard replicas "R", then each shard must have the same number of assigned clusters "N", which is equal to "C" divided by "R". The previous example shows 3 clusters and 3 replicas; therefore, each shard has 1 cluster assigned.
4.2. Enabling dynamic scaling of shards of the Argo CD Application Controller
Dynamic scaling of shards is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.
For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.
By default, the Argo CD Application Controller assigns clusters to shards indefinitely. If you are using the round-robin
sharding algorithm, this static assignment can result in uneven distribution of shards, particularly when replicas are added or removed. You can enable dynamic scaling of shards to automatically adjust the number of shards based on the number of clusters managed by the Argo CD Application Controller at a given time. This ensures that shards are well-balanced and optimizes the use of compute resources.
After you enable dynamic scaling, you cannot manually modify the shard count. The system automatically adjusts the number of shards based on the number of clusters managed by the Argo CD Application Controller at a given time.
4.2.1. Enabling dynamic scaling of shards in the web console
You can enable dynamic scaling of shards by using the OpenShift Container Platform web console.
Prerequisites
-
You have access to the cluster with
cluster-admin
privileges. - You have access to the OpenShift Container Platform web console.
- You have installed the Red Hat OpenShift GitOps Operator on your OpenShift Container Platform cluster.
Procedure
-
In the Administator perspective of the OpenShift Container Platform web console, go to Operators
Installed Operators. - From the the list of Installed Operators, select the Red Hat OpenShift GitOps Operator, and then click the ArgoCD tab.
-
Select the Argo CD instance name for which you want to enable dynamic scaling of shards, for example,
openshift-gitops
. Click the YAML tab, and then edit and configure the
spec.controller.sharding
properties as follows:Example Argo CD YAML file with dynamic scaling enabled
apiVersion: argoproj.io/v1beta1 kind: ArgoCD metadata: name: openshift-gitops namespace: openshift-gitops spec: controller: sharding: dynamicScalingEnabled: true 1 minShards: 1 2 maxShards: 3 3 clustersPerShard: 1 4
- 1
- Set
dynamicScalingEnabled
totrue
to enable dynamic scaling. - 2
- Set
minShards
to the minimum number of shards that you want to have. The value must be set to1
or greater. - 3
- Set
maxShards
to the maximum number of shards that you want to have. The value must be greater than the value ofminShards
. - 4
- Set
clustersPerShard
to the number of clusters that you want to have per shard. The value must be set to1
or greater.
Click Save.
A success notification alert,
openshift-gitops has been updated to version <version>
, appears.NoteIf you edit the default
openshift-gitops
instance, the Managed resource dialog box is displayed. Click Save again to confirm the changes.
Verification
Verify that sharding is enabled by checking the number of pods in the namespace:
-
Go to Workloads
StatefulSets. -
Select the namespace where the Argo CD instance is deployed from the Project drop-down list, for example,
openshift-gitops
. -
Click the name of the
StatefulSet
object that has the name of the Argo CD instance, for exampleopenshift-gitops-apllication-controller
. -
Click the Pods tab, and then verify that the number of pods is equal to or greater than the value of
minShards
that you have set in the Argo CDYAML
file.
4.2.2. Enabling dynamic scaling of shards by using the CLI
You can enable dynamic scaling of shards by using the OpenShift CLI (oc
).
Prerequisites
- You have installed the Red Hat OpenShift GitOps Operator on your OpenShift Container Platform cluster.
-
You have access to the cluster with
cluster-admin
privileges.
Procedure
-
Log in to the cluster by using the
oc
tool as a user withcluster-admin
privileges. Enable dynamic scaling by running the following command:
$ oc patch argocd <argocd_instance> -n <namespace> --type=merge --patch='{"spec":{"controller":{"sharding":{"dynamicScalingEnabled":true,"minShards":<value>,"maxShards":<value>,"clustersPerShard":<value>}}}}'
Example command
$ oc patch argocd openshift-gitops -n openshift-gitops --type=merge --patch='{"spec":{"controller":{"sharding":{"dynamicScalingEnabled":true,"minShards":1,"maxShards":3,"clustersPerShard":1}}}}' 1
- 1
- The example command enables dynamic scaling for the
openshift-gitops
Argo CD instance in theopenshift-gitops
namespace, and sets the minimum number of shards to1
, the maximum number of shards to3
, and the number of clusters per shard to1
. The values ofminShard
andclustersPerShard
must be set to1
or greater. The value ofmaxShard
must be equal to or greater than the value ofminShard
.
Example output
argocd.argoproj.io/openshift-gitops patched
Verification
Check the
spec.controller.sharding
properties of the Argo CD instance:$ oc get argocd <argocd_instance> -n <namespace> -o jsonpath='{.spec.controller.sharding}'
Example command
$ oc get argocd openshift-gitops -n openshift-gitops -o jsonpath='{.spec.controller.sharding}'
Example output when dynamic scaling of shards is enabled
{"dynamicScalingEnabled":true,"minShards":1,"maxShards":3,"clustersPerShard":1}
-
Optional: Verify that dynamic scaling is enabled by checking the configured
spec.controller.sharding
properties in the configurationYAML
file of the Argo CD instance in the OpenShift Container Platform web console. Check the number of Argo CD Application Controller pods:
$ oc get pods -n <namespace> -l app.kubernetes.io/name=<argocd_instance>-application-controller
Example command
$ oc get pods -n openshift-gitops -l app.kubernetes.io/name=openshift-gitops-application-controller
Example output
NAME READY STATUS RESTARTS AGE openshift-gitops-application-controller-0 1/1 Running 0 2m 1
- 1
- The number of Argo CD Application Controller pods must be greater than or equal to the value of
minShard
.