aws_aurora-endpoints.md

AWS RDS Aurora MySQL

AWS RDS Aurora MySQL Cluster (1 instance)

RDS:

• aurora-test (Regional cluster)
  • aurora-test-instance-1 (Writer instance)

Cluster endpoints:

> nslookup aurora-test.cluster-ro-cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 63.34.212.43 --> points to master instance

> nslookup aurora-test.cluster-cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 63.34.212.43 --> points to master instance

Instance endpoints:

> nslookup aurora-test-instance-1.cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 63.34.212.43 --> points to master instance

Adding 1st reader node

RDS:

• aurora-test (Regional cluster)
  • aurora-test-instance-1 (Writer instance)
  • aurora-test-reader (Reader instance)

Cluster endpoints

> nslookup aurora-test.cluster-ro-cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 52.49.243.230 --> points to reader instance

> nslookup aurora-test.cluster-cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 63.34.212.43 --> points to master instance

Instance endpoints:

> nslookup aurora-test-instance-1.cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 63.34.212.43 --> points to master instance

> nslookup aurora-test-reader.cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 52.49.243.230 --> points to reader instance

Adding 2nd reader node

RDS:

• aurora-test (Regional cluster)
  • aurora-test-instance-1 (Writer instance)
  • aurora-test-reader (Reader instance
  • aurora-test-reader-2 (Reader instance)

Cluster endpoints:

> nslookup aurora-test.cluster-ro-cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 52.49.243.230 --> points to reader instance

> nslookup aurora-test.cluster-ro-cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 34.243.226.163 --> points to second reader instance

> nslookup aurora-test.cluster-cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 63.34.212.43 --> points to master instance

Instance endpoints:

> nslookup aurora-test-instance-1.cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 63.34.212.43 --> points to master instance

> nslookup aurora-test-reader.cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 52.49.243.230 --> points to reader instance

> nslookup aurora-test-reader-2.cytaifhqfdcq.eu-west-1.rds.amazonaws.com
...
Address: 34.243.226.163 --> points to second reader instance

Summary

• cluster endpoint points always to master instance (writer)
• cluster read only endpoint points to any of reader instances (load balanced)

ASCII

      [M]   [R] [R]
       |     |   |
       |     \___/
write  |       | read
        \_____/
           |

Terraform Error
The "count" value depends on resource attributes that cannot be determined until apply, so Terraform cannot predict how many instances will be created. To work around
│ this, use the -target argument to first apply only the resources that the count depends on.

My solution maybe not the best but works is to decouple it and not reference needed variable/local/property directly but through remote state

so in XYZ stack

• i export needed value and in the same stack
• terraform apply -refresh-only to write value to state
• I create terraform_remote_state and get value from there
  this way it is decoupled