Archive for December 29th, 2014

29 December, 2014

Two Elasticache Redis Tips

by gorthx

This is all in the Amazon docs about Elasticache Redis. In case you don’t read them, or have inherited a system, and want to keep your data, allow me to share what I learned this week:

1. Make sure you have appendonly enabled1. It is not enabled by default. Turning this on writes all changes to your data to an external file (AOF, for ‘append only file’). Without this, your database only exists in memory. So guess what happens when your instance reboots2? Say bye-bye to your data and hello to restoring from a backup.

Which brings me to item #2:

2. You can’t restore to an existing instance, of course – you have to delete the instance first, then restore. However, deleting the instance also deletes all automated snapshots associated with that instance. This can be a bit surprising. (The ‘are you sure you want to delete this instance’ message does not includes this information.) What I’ve done to get around this is make a manual copy of the automated snapshot I want to restore, prior to deleting the instance. Manual snapshots will stick around until you delete them, regardless of the status of the instance. IME.

You also probably want to configure the Multi-AZ failover, now that it’s available. (

1 –
2 – Keep in mind that this is a managed service; you do not have control over whether it reboots or not.