OSSM-4815: Document HA for a mesh #96010

rh-tokeefe · 2025-07-11T15:30:31Z

Affects:

service-mesh-docs-main
service-mesh-docs-3.0
service-mesh-docs-3.1

PR must be merged to service docs main and CP'd back to the 3.0 and 3.1 branches.

Version(s): 3.1

Issue: https://issues.redhat.com/browse/OSSM-4815

Link to docs preview:
https://96010--ocpdocs-pr.netlify.app/openshift-service-mesh/latest/install/ossm-installing-openshift-service-mesh.html#ossm-about-istio-high-availability_ossm-customizing-istio-configuration

QE review:

QE has approved this change.

Additional information:

openshift-ci-robot · 2025-07-11T15:30:36Z

@rh-tokeefe: This pull request references OSSM-4815 which is a valid jira issue.

In response to this:

Version(s): 3.1

Issue: https://issues.redhat.com/browse/OSSM-4815

Link to docs preview:

QE review:

QE has approved this change.

Additional information:

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the openshift-eng/jira-lifecycle-plugin repository.

openshift-ci-robot · 2025-07-11T15:32:14Z

@rh-tokeefe: This pull request references OSSM-4815 which is a valid jira issue.

In response to this:

Affects:

service-mesh-docs-main
service-mesh-docs-3.0
service-mesh-docs-3.1

PR must be merged to service docs main and CP'd back to the 3.0 and 3.1 branches.

Version(s): 3.1

Issue: https://issues.redhat.com/browse/OSSM-4815

Link to docs preview:

QE review:

QE has approved this change.

Additional information:

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the openshift-eng/jira-lifecycle-plugin repository.

ocpdocs-previewbot · 2025-07-11T15:37:25Z

🤖 Tue Aug 12 12:40:40 - Prow CI generated the docs preview:

https://96010--ocpdocs-pr.netlify.app/
https://96010--ocpdocs-pr.netlify.app/openshift-service-mesh/latest/install/ossm-installing-openshift-service-mesh.html
https://96010--ocpdocs-pr.netlify.app/openshift-service-mesh/latest/update/ossm-updating-openshift-service-mesh.html

openshift-ci-robot · 2025-07-11T20:23:17Z

@rh-tokeefe: This pull request references OSSM-4815 which is a valid jira issue.

In response to this:

Affects:

service-mesh-docs-main
service-mesh-docs-3.0
service-mesh-docs-3.1

PR must be merged to service docs main and CP'd back to the 3.0 and 3.1 branches.

Version(s): 3.1

Issue: https://issues.redhat.com/browse/OSSM-4815

Link to docs preview:
https://96010--ocpdocs-pr.netlify.app/openshift-service-mesh/latest/install/ossm-installing-openshift-service-mesh.html#ossm-about-istio-high-availability_ossm-customizing-istio-configuration

QE review:

QE has approved this change.

Additional information:

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the openshift-eng/jira-lifecycle-plugin repository.

fjglira

I left some minor changes

fjglira · 2025-07-14T11:40:34Z

modules/ossm-about-istio-high-availability.adoc

+
+Running the {istio} control plane in High Availability (HA) mode prevents single points of failure, and ensures continuous mesh operation even if an `istiod` pod fails. By using HA, if one `istiod` pod becomes unavailable, another one continues to manage and configure the {istio} control plane, preventing service outages or disruptions. HA provides scalability by distributing the control plane workload, enables graceful upgrades, supports disaster recovery operations, and protects against zone-wide mesh outages.
+
+There are two ways for a system administrator to configure HA: by defining replica count or by using autoscaling.


Suggested change

There are two ways for a system administrator to configure HA: by defining replica count or by using autoscaling.

There are two ways for a system administrator to configure HA for the `istiod` deployment:

* Defining a static replica count: This involves setting a fixed number of `istiod` pods, providing a consistent level of redundancy.

* Using autoscaling: This dynamically adjusts the number of `istiod` pods based on observed resource utilization or custom metrics, offering more efficient resource consumption for fluctuating workloads.

I think adding a preview here will be better to give the users a first approach to what the configuration types are

fjglira · 2025-07-14T11:48:43Z

modules/ossm-configuring-istio-ha-autoscaling.adoc

+[id="ossm-configuring-istio-ha-autoscaling_{context}"]
+= Configuring Istio HA by using autoscaling 
+
+Configure the {istio} control plane in High Availability (HA) mode to prevent a single point of failure, and ensure continuous mesh operation even if one of the `istiod` pods fails. Autoscaling defines the minimum and maximum number of {istio} control plane pods that can operate. {ocp-product-title} uses these values to scale the number of control planes in operation in response to the varying number of workloads in the mesh.


Suggested change

Configure the {istio} control plane in High Availability (HA) mode to prevent a single point of failure, and ensure continuous mesh operation even if one of the `istiod` pods fails. Autoscaling defines the minimum and maximum number of {istio} control plane pods that can operate. {ocp-product-title} uses these values to scale the number of control planes in operation in response to the varying number of workloads in the mesh.

Configure the {istio} control plane in High Availability (HA) mode to prevent a single point of failure, and ensure continuous mesh operation even if one of the `istiod` pods fails. Autoscaling defines the minimum and maximum number of {istio} control plane pods that can operate. {ocp-product-title} uses these values to scale the number of control planes in operation based on observed resource utilization (such as CPU or memory) or custom metrics, effectively responding to the varying number of workloads and overall traffic patterns within the mesh.

fjglira · 2025-07-14T12:15:55Z

modules/ossm-configuring-istio-ha-autoscaling.adoc

+<1> Defines the minimum number of {istio} control plane replicas that always run. 
+<2> Defines the maximum number of {istio} control plane replicas, allowing for scaling based on load. To support HA, there must be at least two replicas.


It would be highly beneficial to add a note here describing the specific metrics that can be used to configure Istiod autoscaling (scale up/down). For example, users can set spec.values.pilot.cpu.targetAverageUtilization and spec.values.pilot.memory.targetAverageUtilization to define CPU and Memory thresholds for triggering scaling actions. Sorry for not adding this also in the upstream docs, but I'll add it there. I think it's good to point the users which configuration is going to trigger this

fjglira · 2025-07-14T12:17:19Z

modules/ossm-configuring-istio-ha-autoscaling.adoc

+istiod-7c7b6564c9-xkmsl   1/1     Running   0          85s
+----
+
+Two `istiod` pods are running, which indicates HA was successfully configured.


Suggested change

Two `istiod` pods are running, which indicates HA was successfully configured.

Two `istiod` pods are running, which is the minimum requirement for a highly available Istio control plane and indicates a basic HA setup is in place.

fjglira · 2025-07-14T12:53:46Z

modules/ossm-configuring-istio-ha-replicacount.adoc

+[id="ossm-configuring-istio-ha-replicacount_{context}"]
+= Configuring Istio HA by using replica count
+
+Configure the {istio} control plane in High Availability (HA) mode to prevent a single point of failure, and ensure continuous mesh operation even if one of the `istiod` pods fails. The replica count defines a fixed number of {istio} control plane pods that can operate. Use replica count for mesh environments in which the number of workloads does not scale.


Suggested change

Configure the {istio} control plane in High Availability (HA) mode to prevent a single point of failure, and ensure continuous mesh operation even if one of the `istiod` pods fails. The replica count defines a fixed number of {istio} control plane pods that can operate. Use replica count for mesh environments in which the number of workloads does not scale.

Configure the {istio} control plane in High Availability (HA) mode to prevent a single point of failure, and ensure continuous mesh operation even if one of the `istiod` pods fails. The replica count defines a fixed number of {istio} control plane pods that can operate. Use replica count for mesh environments where the control plane workload is relatively stable or predictable, or when manual scaling of the `istiod` is preferred.

fjglira

lgtm, this looks great with the updated procedure

FilipB · 2025-07-23T12:32:44Z

modules/ossm-about-istio-high-availability.adoc

+[id="ossm-about-istio-high-availability_{context}"]
+= About Istio High Availability
+
+Running the {istio} control plane in High Availability (HA) mode prevents single points of failure, and ensures continuous mesh operation even if an `istiod` pod fails. By using HA, if one `istiod` pod becomes unavailable, another one continues to manage and configure the {istio} control plane, preventing service outages or disruptions. HA provides scalability by distributing the control plane workload, enables graceful upgrades, supports disaster recovery operations, and protects against zone-wide mesh outages.


"another one continues to manage and configure the Istio control plane"
Should that be "continues to manage and configure the Istio data plane"?

Yes, my bad we should said here:

Running the {istio} control plane in High Availability (HA) mode prevents single points of failure, and ensures continuous mesh operation even if an `istiod` pod fails. By using HA, if one `istiod` pod becomes unavailable, another one continues to manage and configure the {istio} data plane, preventing service outages or disruptions. HA provides scalability by distributing the control plane workload, enables graceful upgrades, supports disaster recovery operations, and protects against zone-wide mesh outages.

@FilipB and @fjglira just want to check with you about this part:

"HA provides scalability by distributing the control plane workload..."

Do we keep control plane here or also change this to data plane?

"HA provides scalability by distributing the control plane workload..." part is correct. There is multiple istiod instasnces and istiod == control plane. Istiod (control plane) is managing data plane.

FilipB · 2025-07-23T12:39:07Z

modules/ossm-api-settings-mesh-ha-autoscaling.adoc

+
+|`autoScaleMin` | Defines the minimum number of `istiod` pods for an istio deployment. Each pod contains one instance of the Istio control plane. 
+
+{ocp-short-name} only uses this parameter when the {istio} deployment uses the Horizontal Pod Autoscaler (HPA) configuration. 


This note is a bit confusing. Creation of HPA is controlled by Values.autoscaleEnabled

Yeah, and this is a table that shows all the parameters available to configure for HA deployment. Maybe we should say:

{ocp-short-name} only uses this parameter when Horizontal Pod Autoscaler (HPA) is enabled for the {istio} deployment, which is the default behavior (Values.autoscaleEnabled: true).

fjglira · 2025-07-28T13:13:51Z

modules/ossm-api-settings-mesh-ha-autoscaling.adoc

+
+|`autoScaleMin` | Defines the minimum number of `istiod` pods for an istio deployment. Each pod contains one instance of the Istio control plane. 
+
+{ocp-short-name} only uses this parameter when the {istio} deployment uses the Horizontal Pod Autoscaler (HPA) configuration. 


Yeah, and this is a table that shows all the parameters available to configure for HA deployment. Maybe we should say:

{ocp-short-name} only uses this parameter when Horizontal Pod Autoscaler (HPA) is enabled for the {istio} deployment, which is the default behavior (Values.autoscaleEnabled: true).

fjglira · 2025-07-28T13:14:28Z

modules/ossm-api-settings-mesh-ha-autoscaling.adoc

+
+You must also configure metrics for autoscaling to work properly. If no metrics are configured, the autoscaler does not scale up or down.
+
+{ocp-short-name} only uses this parameter when the {istio} deployment uses the HPA configuration. 


Same here then:

{ocp-short-name} only uses this parameter when Horizontal Pod Autoscaler (HPA) is enabled for the {istio} deployment, which is the default behavior (Values.autoscaleEnabled: true).

FilipB · 2025-07-30T07:36:13Z

modules/ossm-about-istio-high-availability.adoc

+[id="ossm-about-istio-high-availability_{context}"]
+= About Istio High Availability
+
+Running the {istio} control plane in High Availability (HA) mode prevents single points of failure, and ensures continuous mesh operation even if an `istiod` pod fails. By using HA, if one `istiod` pod becomes unavailable, another one continues to manage and configure the {istio} data plane, preventing service outages or disruptions. HA provides scalability by distributing the control plane workload, enables graceful upgrades, supports disaster recovery operations, and protects against zone-wide mesh outages.


"By using HA, if one istiod pod becomes unavailable, another one continues..."
@rh-tokeefe does this make sense or it should be rephrased?

@FilipB "By using" conforms to the style guide.

All I'm trying to say here is "When using HA, if one istiod pod becomes unavailable, another one continues to manage and configure the {istio} data plane, preventing service outages or disruptions."

We can sync and chat if you'd like.

It's fine I was just not sure if it is good English grammar.

shreyasiddhartha

Hi @rh-tokeefe!
I only have a few comments related to the OCP guidelines. Overall. LGTM.
Please reach out to me if you have any questions. :)

shreyasiddhartha · 2025-08-07T06:45:43Z

install/ossm-installing-openshift-service-mesh.adoc

+
+[role="_additional-resources-pod-scaling"]
+.Additional resources
+* link:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/[Horizontal Pod Autoscaling]


Suggested change

* link:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/[Horizontal Pod Autoscaling]

* link:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/[Horizontal Pod Autoscaling (Kubernetes documentation)]

* link:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/#configurable-scaling-behavior[Configurable Scaling Behavior (Kubernetes documentation)]

Suggestion to provide the source of external links, if the link is not from our product docs.
I also added a suggestion to adda link here from another instance where a link was used in the module ossm-api-settings-mesh-ha-autoscaling.adoc.

shreyasiddhartha · 2025-08-07T06:46:12Z

modules/ossm-api-settings-mesh-ha-autoscaling.adoc

+|===
+|Parameter |Description 
+
+|`autoScaleMin` | Defines the minimum number of `istiod` pods for an istio deployment. Each pod contains one instance of the Istio control plane. 


Suggested change

|`autoScaleMin` | Defines the minimum number of `istiod` pods for an istio deployment. Each pod contains one instance of the Istio control plane.

|`autoScaleMin` | Defines the minimum number of `istiod` pods for an {istio} deployment. Each pod contains one instance of the {istio} control plane.

Suggestion to use the {istio} attribute here.

shreyasiddhartha · 2025-08-07T06:52:09Z

modules/ossm-api-settings-mesh-ha-autoscaling.adoc

+|`memory.targetAverageUtilization` | Defines the target memory utilization for the `istiod` pod. If the average memory usage exceeds the threshold that this parameter defines, the HPA automatically increases the number of replica pods.
+|`behavior` | You can use the `behavior` field to define additional policies that {ocp-short-name} uses to scale {istio} resources up or down.
+
+For more information, see link:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/#configurable-scaling-behavior[Configurable Scaling Behavior].


Suggested change

For more information, see link:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/#configurable-scaling-behavior[Configurable Scaling Behavior].

For more information, see "Configurable Scaling Behavior".

Just a suggestion to provide the link in the "Additional resources" section rather than the module. I will update the suggestion in the assembly file as well.

shreyasiddhartha · 2025-08-07T07:00:17Z

modules/ossm-api-settings-mesh-ha-replicacount.adoc

+|===
+|Parameter |Description 
+
+|`replicaCount` | Defines the number of `istiod` pods for an istio deployment. Each pod contains one instance of the `istio` control plane. The default setting is `1`.


Suggested change

|`replicaCount` | Defines the number of `istiod` pods for an istio deployment. Each pod contains one instance of the `istio` control plane. The default setting is `1`.

|`replicaCount` | Defines the number of `istiod` pods for an {istio} deployment. Each pod contains one instance of the {istio} control plane. The default setting is `1`.

I have a confusion regarding the usage of the following:

Istio control plane or Istio control plane

Istio deployment or Istio deployment

I will leave it up to you to decide. My only suggestion is to make it consistent throughout and also the usage of {istio} attribute.

shreyasiddhartha · 2025-08-07T07:02:01Z

modules/ossm-configuring-istio-ha-autoscaling.adoc

+
+* You installed the {SMProductName} Operator.
+
+* You deployed the {istio} resource.


Suggested change

* You deployed the {istio} resource.

* You have deployed the `{istio}` resource.

Suggestion to add code blocks here.

shreyasiddhartha · 2025-08-07T07:27:46Z

modules/ossm-configuring-istio-ha-replicacount.adoc

+default   1           1       0        default           Healthy   v1.24.6   24m
+----
+
+The name of the {istio} resource is `default`.


Suggested change

The name of the {istio} resource is `default`.

The name of the `{istio}` resource is `default`.

shreyasiddhartha · 2025-08-07T07:28:06Z

modules/ossm-configuring-istio-ha-replicacount.adoc

+
+The name of the {istio} resource is `default`.
+
+. Update the {istio} custom resource by adding the `autoscaleEnabled` and `replicaCount` parameters by running the following command:


Suggested change

. Update the {istio} custom resource by adding the `autoscaleEnabled` and `replicaCount` parameters by running the following command:

. Update the `{istio}` custom resource (CR) by adding the `autoscaleEnabled` and `replicaCount` parameters by running the following command:

shreyasiddhartha · 2025-08-07T07:32:35Z

modules/ossm-configuring-istio-ha-replicacount.adoc

+<1> Disables autoscaling and ensures that the number of replicas remains fixed.
+<2> Defines the number of {istio} control plane replicas. To support HA, there must be at least two replicas.


Suggested change

<1> Disables autoscaling and ensures that the number of replicas remains fixed.

<2> Defines the number of {istio} control plane replicas. To support HA, there must be at least two replicas.

<1> Specifies a setting that disables autoscaling and ensures a fixed number of replicas.

<2> Specifies the number of {istio} control plane replicas. To support HA, there must be at least two replicas.

shreyasiddhartha · 2025-08-07T07:36:34Z

modules/ossm-configuring-istio-ha-autoscaling.adoc

+
+.Verification
+
+. Verify the status of the {istio} control pods by running the following command:


Suggested change

. Verify the status of the {istio} control pods by running the following command:

* Verify the status of the {istio} control pods by running the following command:

Since this is a single step procedure, I think it is okay to not make it a numbered-list. Here's the guideline.

shreyasiddhartha · 2025-08-07T07:37:21Z

modules/ossm-configuring-istio-ha-replicacount.adoc

+
+.Verification
+
+. Verify the status of the {Istio} control pods by running the following command:


Suggested change

. Verify the status of the {Istio} control pods by running the following command:

* Verify the status of the {Istio} control pods by running the following command:

openshift-ci · 2025-08-12T12:42:42Z

@rh-tokeefe: all tests passed!

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rh-tokeefe · 2025-08-12T13:20:52Z

/cherrypick service-mesh-docs-3.1

rh-tokeefe · 2025-08-12T13:21:03Z

/cherrypick service-mesh-docs-3.0

openshift-cherrypick-robot · 2025-08-12T13:21:40Z

@rh-tokeefe: new pull request created: #97438

In response to this:

/cherrypick service-mesh-docs-3.1

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openshift-cherrypick-robot · 2025-08-12T13:21:50Z

@rh-tokeefe: new pull request created: #97439

In response to this:

/cherrypick service-mesh-docs-3.0

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rh-tokeefe · 2025-08-12T19:13:32Z

/cherrypick service-mesh-docs-3.1

openshift-cherrypick-robot · 2025-08-12T19:14:22Z

@rh-tokeefe: new pull request could not be created: failed to create pull request against openshift/openshift-docs#service-mesh-docs-3.1 from head openshift-cherrypick-robot:cherry-pick-96010-to-service-mesh-docs-3.1: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for openshift-cherrypick-robot:cherry-pick-96010-to-service-mesh-docs-3.1."}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request","status":"422"}

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/cherrypick service-mesh-docs-3.1

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OSSM-4815: Document HA for a mesh

56f92f7

rh-tokeefe force-pushed the OSSM-4815 branch from ca36f60 to 56f92f7 Compare August 12, 2025 12:30

rh-tokeefe merged commit 4754a15 into openshift:service-mesh-docs-main Aug 12, 2025
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[service-mesh-docs-3.1] OSSM-4815: Document HA for a mesh #97438

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[service-mesh-docs-3.0] OSSM-4815: Document HA for a mesh #97439

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		Running the {istio} control plane in High Availability (HA) mode prevents single points of failure, and ensures continuous mesh operation even if an `istiod` pod fails. By using HA, if one `istiod` pod becomes unavailable, another one continues to manage and configure the {istio} control plane, preventing service outages or disruptions. HA provides scalability by distributing the control plane workload, enables graceful upgrades, supports disaster recovery operations, and protects against zone-wide mesh outages.

		There are two ways for a system administrator to configure HA: by defining replica count or by using autoscaling.

-There are two ways for a system administrator to configure HA: by defining replica count or by using autoscaling.
+There are two ways for a system administrator to configure HA for the `istiod` deployment:
+* Defining a static replica count: This involves setting a fixed number of `istiod` pods, providing a consistent level of redundancy.
+* Using autoscaling: This dynamically adjusts the number of `istiod` pods based on observed resource utilization or custom metrics, offering more efficient resource consumption for fluctuating workloads.

		<1> Defines the minimum number of {istio} control plane replicas that always run.
		<2> Defines the maximum number of {istio} control plane replicas, allowing for scaling based on load. To support HA, there must be at least two replicas.

	Two `istiod` pods are running, which indicates HA was successfully configured.
	Two `istiod` pods are running, which is the minimum requirement for a highly available Istio control plane and indicates a basic HA setup is in place.


		\|`autoScaleMin` \| Defines the minimum number of `istiod` pods for an istio deployment. Each pod contains one instance of the Istio control plane.

		{ocp-short-name} only uses this parameter when the {istio} deployment uses the Horizontal Pod Autoscaler (HPA) configuration.


		You must also configure metrics for autoscaling to work properly. If no metrics are configured, the autoscaler does not scale up or down.

		{ocp-short-name} only uses this parameter when the {istio} deployment uses the HPA configuration.

	* link:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/[Horizontal Pod Autoscaling]
	* link:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/[Horizontal Pod Autoscaling (Kubernetes documentation)]
	* link:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/#configurable-scaling-behavior[Configurable Scaling Behavior (Kubernetes documentation)]

	For more information, see link:https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/#configurable-scaling-behavior[Configurable Scaling Behavior].
	For more information, see "Configurable Scaling Behavior".

	\|`replicaCount` \| Defines the number of `istiod` pods for an istio deployment. Each pod contains one instance of the `istio` control plane. The default setting is `1`.
	\|`replicaCount` \| Defines the number of `istiod` pods for an {istio} deployment. Each pod contains one instance of the {istio} control plane. The default setting is `1`.


		* You installed the {SMProductName} Operator.

		* You deployed the {istio} resource.

	* You deployed the {istio} resource.
	* You have deployed the `{istio}` resource.

	The name of the {istio} resource is `default`.
	The name of the `{istio}` resource is `default`.

	. Update the {istio} custom resource by adding the `autoscaleEnabled` and `replicaCount` parameters by running the following command:
	. Update the `{istio}` custom resource (CR) by adding the `autoscaleEnabled` and `replicaCount` parameters by running the following command:

		<1> Disables autoscaling and ensures that the number of replicas remains fixed.
		<2> Defines the number of {istio} control plane replicas. To support HA, there must be at least two replicas.


		.Verification

		. Verify the status of the {istio} control pods by running the following command:

	. Verify the status of the {istio} control pods by running the following command:
	* Verify the status of the {istio} control pods by running the following command:

OSSM-4815: Document HA for a mesh #96010

OSSM-4815: Document HA for a mesh #96010

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rh-tokeefe commented Jul 11, 2025 •

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