How to check via aws cli if a specific rds instance exists?

Question

I want my bash script to detect, if an AWS RDS instance with a specific name exists already.

This is what I tried:

 #!/usr/bin/env bash DBINSTANCEIDENTIFIER=greatdb EXISTINGINSTANCE=$(aws rds describe-db-instances \ --db-instance-identifier="$DBINSTANCEIDENTIFIER" \ --output text\ ) 

I would expect an empty list, or a zero as a result - but I receive an error message:

 An error occurred (DBInstanceNotFound) when calling the DescribeDBInstances operation: DBInstance greatdb not found. 

Does anyone know how to properly find out if an instance exists or not, without an error message?

Answer 1

Notice the constraint in the docs when using --db-instance-indentifier:

--db-instance-identifier (string) The user-supplied instance identifier. If this parameter is specified, information from only the specific DB instance is returned. This parameter isn't case-sensitive. Constraints: - If supplied, must match the identifier of an existing DBInstance 

So you can only use this option if you know the DB in fact exists.

Using queries

To search for a DB that may or may not exist you'll have to use the --query option:

$ aws rds describe-db-instances \ --query 'DBInstances[*].[DBName,DBInstanceIdentifier]' --output text 

The DBINstances JSON structure is accessible in the awscli help:

$ aws rds describe-db-instances help --output text ... ... { "DBInstances": [ { "PubliclyAccessible": false, "MasterUsername": "mymasteruser", "MonitoringInterval": 0, "LicenseModel": "general-public-license", ... ... "DBName": "sample", ... ... "DBInstanceStatus": "stopped", "EngineVersion": "5.6.27", "AvailabilityZone": "us-east-1e", "StorageType": "standard", "StorageEncrypted": false, "DBInstanceClass": "db.t2.micro", "DbInstancePort": 0, "DBInstanceIdentifier": "mydbinstance-1" } ] } ... ... 

Using Filters

Another simple solution for the initial question is, to use the --filters parameter. The query will return either the instance identifier (if the instance exists), or an empty string (if it does not exist):

 #!/usr/bin/env bash DBINSTANCEIDENTIFIER="greatdb" EXISTINGINSTANCE=$(aws rds describe-db-instances \ --query 'DBInstances[*].[DBInstanceIdentifier]' \ --filters Name=db-instance-id,Values=$DBINSTANCEIDENTIFIER \ --output text \ ) if [ -z $EXISTINGINSTANCE ] then echo "instance $DBINSTANCEIDENTIFIER does not exist!" else echo "instance $DBINSTANCEIDENTIFIER exists!" fi 

References

• https://docs.aws.amazon.com/cli/latest/reference/rds/describe-db-instances.html
• https://stackoverflow.com/questions/45449174/how-do-i-use-query-parameter-in-aws-rds-describe-db-instances-command
• https://stackoverflow.com/questions/46051538/syntax-for-filters-for-aws-rds-describe-db-instances