In this post we are going to go over the best practises for taking a snapshot¹ of a 2 VMware vCenter Server Appliance (VCSA)² instances that are in enhanced linked mode.

NOTE: This post does not go into a “how to” of taking a VCSA snapshot, instead it focuses on what you need to make sure you do when taking a snapshot and then rolling back.

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1. SECTION I – Why It Matters?
2. SECTION II – Taking Snapshot
   1. SECTION II – A – Snapshot Best Practise
   2. SECTION II – B – Quick Snapshot
3. SECTION III – Safe Rollback
4. SECTION IV – Footnotes

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SECTION I – Why It Matters?

When you have multiple VCSA instances in enhanced link mode they will send communication messages between each other. Some of these updates are for replication of the VMDir PostgreSQL database to keep it in sync between the sites. Each instance will keep track of the sequence number of messages both sent and received to and from a replication partner.

An issue arises when you take an improper snapshot of a VCSA instance and then choose to roll one of the instances back and not the other. This is because the rolled back instance is going to start sending replication messages that the other instance thinks it has already received. If this happens and isn’t rectified then it doesn’t take long for the VCSA instances to fall out of replication and either site may put its VMDir into read only mode as a way to protect itself which can stop the VCSA instance for working properly.

SECTION II – Taking Snapshot

SECTION II – A – Snapshot Best Practise

The best practise when taking a snapshot of VCSA instances in enhanced linked mode is to:

1. If High Availability (HA) mode is enabled when disable HA.
2. Power off both VCSA instances.
3. Utilising the hypervisor where the VCSA instance VM is, take a snapshot of the VCSA Virtual Machine (VM).
4. Power on both VCSA instances.

SECTION II – B – Quick Snapshot

If you need to take a snapshot in a hurry and cannot wait for both VCSA instances to power off and then back on then you can do the following:

1. If HA mode is enabled when disable HA.
2. With both VCSA instances powered on.
3. Utilising the hypervisor where the VCSA instance VM is, take a snapshot of the VCSA VM making sure to not capture the memory.

SECTION III – Safe Rollback

Now if you need to utilise the snapshots you made for any reason such as a update failing on one of the VCSA instances then the only thing you need to make sure you do is roll both VCSA instances back to their snapshots taking in Section II at the same time. This will avoid the PostgreSQL database replication breaking between the VCSA instances that are in enhanced linked mode.

SECTION IV – Footnotes

1. Snapshot – this is a point in time of all the data on a specific VM. It allows for you to return a VMs data to the specific point in time when its snapshot was taken. Memory can be included in the snapshot as well. ↩︎
2. vCenter Server Appliance – A dedicated server designed to run vCetner Server. vCenter Server is a centralised management platform for multiple vSphere (ESXi) instances. ↩︎