While updating agentPools need to check for only fields which are mutable.

[LochanRn]

/kind bug
/area managedclusters
What steps did you take and what happened:
[A clear and concise description of what the bug is.]
When an update is triggered for agentpools the agentpool service compares the exiting agentPool and the updated agentPool
before it actually makes a CreateOrUpdate api call.

cluster-api-provider-azure/azure/services/agentpools/agentpools.go

Lines 88 to 101 in 40fde82

	existingProfile := containerservice.AgentPool{
	ManagedClusterAgentPoolProfileProperties: &containerservice.ManagedClusterAgentPoolProfileProperties{
	VMSize: existingPool.ManagedClusterAgentPoolProfileProperties.VMSize,
	OsType: containerservice.Linux,
	OsDiskSizeGB: existingPool.ManagedClusterAgentPoolProfileProperties.OsDiskSizeGB,
	Count: existingPool.ManagedClusterAgentPoolProfileProperties.Count,
	Type: containerservice.VirtualMachineScaleSets,
	OrchestratorVersion: existingPool.ManagedClusterAgentPoolProfileProperties.OrchestratorVersion,
	VnetSubnetID: existingPool.ManagedClusterAgentPoolProfileProperties.VnetSubnetID,
	},
	}
	// Diff and check if we require an update
	diff := cmp.Diff(profile, existingProfile)

The current logic checks for the all the fields while comparison, most of the fields are immutable and should be avoided.

The fields for which AKS supports mutating are

• k8sVersion
• count
• mode

What did you expect to happen:
The right way to implement it would be:

existingProfile := containerservice.AgentPool{
	ManagedClusterAgentPoolProfileProperties: &containerservice.ManagedClusterAgentPoolProfileProperties{
		Count:               existingPool.Count,
		OrchestratorVersion: existingPool.OrchestratorVersion,
		Mode:                existingPool.Mode,
	},
}

normalizedProfile := containerservice.AgentPool{
	ManagedClusterAgentPoolProfileProperties: &containerservice.ManagedClusterAgentPoolProfileProperties{
		Count:               profile.Count,
		OrchestratorVersion: profile.OrchestratorVersion,
		Mode:                profile.Mode,
	},
}

// Diff and check if we require an update
diff := cmp.Diff(existingProfile, normalizedProfile)

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• cluster-api-provider-azure version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[CecileRobertMichon]

@LochanRn are you taking this one or should we mark it as good-first-issue?

/area managedclusters

[LochanRn]

I have added a fix for this in the system-node-pool PR.

[CecileRobertMichon]

/assign @LochanRn