RDS Notes

Posted: 05 June, 2020 Category: rough notes Tagged: rdsaws

I have surprisingly little in the way of jotted notes about RDS thus far. Like EC2, it's very "does what it says on the tin": you create an RDS instance, you choose your database engine... and that's preeetty much it.

Random jottings on RDS

  • Uses a an EC2 instance under the hood (eg a db.t2.micro), but it's special in that you can't log in to it
  • you can seed yourdb with the initial database name if you need to.
  • You need to turn on backups if you want any kind of replication to take place. Related to which:
  • Backups are fully automated (unlike manual snapshots)
  • Manual snapshot: (rds instance) > Actions create snapshot...
  • There are read replicas (asynchronous replication) and they can be anywhere (any AZ, region etc). Goto (rds instance) > Actions > create read replica...

Moving RDS instances between VPCs: Maybe just.. don't.

Finnickier than I'd have thought. I expected to be just able to modify the instance and change the network settings to use my VPC and desired private subnet. I couldn't select a subnet corresponding to my VPC though. This article might be helpful. In my case:

  • My AZ's were a total mismatch (I remember letting AWS pick the AZs for my subnets lol)
  • RDS requires the subnet it's in to have 2 different AZs... so I had to go back and create an extra subnet in a different AZ before I could move my RDS instance into my VPC.

The following didn't work, but gives you an idea of what's going on under the hood

Following the article I linked to, I tried this:

  • Create a new DB Subnet group first (under RDS)
  • Select the desired VPC
  • Select the correct pair of AZs which matched the ones used by subnets... THEN it finally listed my subnets so I could pick the ones I wanted. You have to be careful to pick your private subnets in this step... you'll be staring at some unfriendly Ids. KNOW WHICH ONES ARE WHICH.
  • goto (rds instance) > Modify
  • under Network and Security, select:

    • your new db subnet group
    • The security group you created for dbs in your private subnets (You have one right?)

That should work... Unless like me, you still have a mismatched AZ kicking around somewhere (for me, it seemed to be the RDS instance itself).

Update 2020-06-08 They've literally just updated the RDS creation page. It now clearly states that you can't be muffing about with the target VPC after you've created your instance. Honestly I just scrapped my DB and recreated it, targeting the right VPC, the db subnet group I'd created in the steps above, and the correct security group..

The data store ecosystem

  • Redshift: best for OLAP:

    • advanced features like compression, distributed query loads, etc. You should read up on it.
    • own security key management
  • Aurora DB: serverless; pay per-invocation
  • Dynamo DB: the AWS noSQL solution
  • Elasticache: memory-based, so faster than disk-based fetches. Uses Memcached (simple) or Redos (advanced) under the hood.