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Failover in Managed Service for TimescaleDB

One standby read-only replica server is configured, for each Managed Service for TimescaleDB on a Pro plan. You can query a read-only replica server, but cannot write to a read-only replica server. When a master server fails, the standby replica server is automatically promoted as master. If you manually created a read-only replica service, then if a master server fails, the read-only replica services are not promoted as master servers.

The two distinct cases during which failovers occur are:

  • When the master or replica fails unexpectedly, for example because the hardware hosting the virtual machine fails.
  • When controlled failover happens because of upgrades.

Uncontrolled master or replica fail

When a replica server fails unexpectedly, there is no way to know whether the server really failed, or whether there is a temporary network glitch with the cloud provider's network.

There is a 300 seconds timeout before Managed Service for TimescaleDB automatically decides the server is gone and spins up a new replica server. During these 300 seconds, replica.servicename.timescaledb.io points to a server that may not serve queries anymore. The DNS record pointing to the master server servicename.timescaledb.io continues to serve the queries. If the replica server does not come back up within 300 seconds, replica.servicename.timescaledb.io points to the master server, until a new replica server is built.

When the master server fails, a replica server waits for 60 seconds before promoting itself as master. During this 60-second timeout, the master server servicename.timescaledb.io remains unavailable and does not respond. However, replica.servicename.timescaledb.io works in read-only mode. After the replica server promotes itself as master, servicename.timescaledb.io points to the new master server, and replica.servicename.timescaledb.io continues to point to the new master server. A new replica server is built automatically, and after it is in sync, replica.servicename.timescaledb.io points to the new replica server.

Controlled failover during upgrades

When applying upgrades or plan changes on business or premium plans, the standby server is replaced:

A new server is started, the backup is restored, and the new server starts following the old master server. After the new server is up and running, replica.servicename.timescaledb.io is updated, and the old replica server is deleted.

For premium plans, this step is executed for both replica servers before the master server is replaced. Two new servers are started, a backup is restored, and one new server is synced up to the old master server. When it is time to switch the master to a new server, the old master is terminated and one of the new replica servers is immediately promoted as a master. At this point, servicename.timescaledb.io is updated to point at the new master server. Similarly, the new master is removed from the replica.servicename.timescaledb.io record.

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