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OSSM-4815: Document HA for a mesh #96010

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4 changes: 4 additions & 0 deletions install/ossm-installing-openshift-service-mesh.adoc
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Expand Up @@ -46,3 +46,7 @@ include::modules/ossm-accessing-bookinfo-application-using-gateway-api.adoc[leve
* link:https://docs.redhat.com/en/documentation/openshift_container_platform/latest/html/networking/configuring-ingress-cluster-traffic[Configuring ingress cluster traffic]

include::modules/ossm-customizing-istio-configuration.adoc[leveloffset=+1]

include::modules/ossm-about-istio-high-availability.adoc[leveloffset=+1]
include::modules/ossm-configuring-istio-ha-autoscaling.adoc[leveloffset=+2]
include::modules/ossm-configuring-istio-ha-replicacount.adoc[leveloffset=+2]
10 changes: 10 additions & 0 deletions modules/ossm-about-istio-high-availability.adoc
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// This module is used in the following assemblies:
// * service-mesh-docs-main/install/ossm-installing-service-mesh.adoc

:_mod-docs-content-type: CONCEPT
[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.

There are two ways for a system administrator to configure HA: by defining replica count or by using autoscaling.
68 changes: 68 additions & 0 deletions modules/ossm-configuring-istio-ha-autoscaling.adoc
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// This procedure is used in the following assembly:
// * service-mesh-docs-main/install/ossm-installing-service-mesh.adoc

:_mod-docs-content-type: PROCEDURE
[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.

.Prerequisites

* You are logged in to the {ocp-product-title} web console as a user with the `cluster-admin` role.

* You installed the {SMProductName} Operator.

* You deployed the {istio} resource.

.Procedure

. Obtain the name of the {istio} resource by running the following command:
+
[source,terminal]
----
$ oc get istio -n istio-system
----
+
.Example output
[source,terminal]
----
NAME REVISIONS READY IN USE ACTIVE REVISION STATUS VERSION AGE
default 1 1 0 default Healthy v1.24.6 24m
----
+
The name of the {istio} resource is `default`.

. Update the {istio} custom resource by adding the `autoscaleMin` and `autoscaleMax` parameters by running the following command:
+
[source,terminal]
----
$ oc patch istio default -n istio-system --type merge -p '
spec:
values:
pilot:
autoscaleMin: 2 <1>
autoscaleMax: 5 <2>
'
----
<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.

.Verification

. Verify the status of the {Istio} control pods by running the following command:
+
[source,terminal]
----
$ oc get pods -n istio-system -l app=istiod
----
+
.Example output
[source,terminal]
----
NAME READY STATUS RESTARTS AGE
istiod-7c7b6564c9-nwhsg 1/1 Running 0 70s
istiod-7c7b6564c9-xkmsl 1/1 Running 0 85s
----
+
Two `istiod` pods are running, which indicates HA was successfully configured.
68 changes: 68 additions & 0 deletions modules/ossm-configuring-istio-ha-replicacount.adoc
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// This procedure is used in the following assembly:
// * service-mesh-docs-main/install/ossm-installing-service-mesh.adoc

:_mod-docs-content-type: PROCEDURE
[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.

.Prerequisites

* You are logged in to the {ocp-product-title} web console as a user with the `cluster-admin` role.

* You installed the {SMProductName} Operator.

* You deployed the {istio} resource.

.Procedure

. Obtain the name of the {istio} resource by running the following command:
+
[source,terminal]
----
$ oc get istio -n istio-sytem
----
+
.Example output
[source,terminal]
----
NAME REVISIONS READY IN USE ACTIVE REVISION STATUS VERSION AGE
default 1 1 0 default Healthy v1.24.6 24m
----
+
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:
+
[source,terminal]
----
$ oc patch istio default -n istio-system --type merge -p '
spec:
values:
pilot:
autoscaleEnabled: false <1>
replicaCount: 2 <2>
'
----
<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:
+
[source,terminal]
----
$ oc get pods -n istio-system -l app=istiod
----
+
.Example output
[source,terminal]
----
NAME READY STATUS RESTARTS AGE
istiod-7c7b6564c9-nwhsg 1/1 Running 0 70s
istiod-7c7b6564c9-xkmsl 1/1 Running 0 85s
----
+
Two `istiod` pods are running, which indicates HA was successfully configured.