/amazon-aurora-mysql

Aurora serverless — Worked Examples and Scale-to-Zero Rules

Companion to instructions.md and formulas-and-examples.md. The formulas and pricing tables used to produce these numbers live in formulas-and-examples.md.

Worked example — basic sizing

User asks: db.r6g.xlarge, CPU P95 35%, max 72%, 500 GiB storage, should I switch to Aurora serverless? Region: us-east-1.

Agent reply should follow this pattern — present the script output, no derivation shown:

"Loading references/serverless-advisory-instructions.md — this is the serverless sizing workflow.

The command to run this analysis yourself from a machine with Python 3.10+ and boto3 installed:

python3 scripts/acu_calculator.py estimate \
  --instance db.r6g.xlarge --cpu-p95 35 --cpu-max 72 --storage 500 --region us-east-1

Running that with your parameters produces:

Metric	Value
min ACU	3.5
max ACU	16.0
typical ACU	6.0
Peak ACU vs 256 ceiling	Well under (12.0/256)

Monthly cost	Amount
Provisioned db.r6g.xlarge compute	$379
Aurora serverless at typical ACU compute	$526
Aurora serverless total range (min–max, incl. storage)	$357–$1,452
Storage (500 GiB × $0.10)	$50
Total Provisioned / Total Aurora serverless (typical)	$429 / $576

Recommendation: not_recommended. At typical load, Aurora serverless is ~34% more expensive than provisioned ($576 vs $429). Your workload (P95 35%, max 72%) is steady — the burst/idle pattern that makes serverless win isn't present. Stay on db.r6g.xlarge. If you want the savings anyway, consider a 1-year RI on the provisioned instance (~30% off compute), which brings total to ~$315/mo."

Note what this reply does NOT include: no "0.21 × 4 × 4 = 3.36, round up to 3.5" arithmetic; no formula derivation; no "here's how I computed it." Just the script-style output.

(The internal formulas for producing these numbers are in formulas-and-examples.md. Use them to generate the output, but don't copy them into the reply.)

Worked example — migration with connection and working-set constraints

User: db.r7g.2xlarge, 200 peak connections, 12 GiB working set, P95 40%, max 65%, 1 TB storage, region eu-west-1. Walk through the whole thing.

Agent response pattern (abridged):

1. Announce reference: "Loading references/serverless-advisory-instructions.md."

2. Print:

   python3 scripts/acu_calculator.py estimate \
     --region eu-west-1 \
     --instance db.r7g.2xlarge \
     --cpu-p95 40 --cpu-max 65 \
     --connections 200 --working-set 12 --storage 1000 \
     --num-instances 1 --format table

3. Script output (db.r7g.2xlarge, 8 vCPU): min_ACU 8.0 (working-set floor 12/2 = 6.0 is satisfied), peak_ACU 21.0, max_ACU 27.5 (= max(round_up(21.0 × 1.30), round_up(13.5 × 1.50))), typical_ACU 13.5.

4. Costs: offline/static mode prices at us-east-1 rates ($0.12/ACU-hr, $0.10/GiB-mo storage) regardless of --region; only live API mode applies the eu-west-1 rate. Aurora serverless typical 13.5 × $0.12 × 730 = $1,183/mo compute, storage 1000 × $0.10 = $100, total**$1,283/mo**. Provisioned r7g.2xlarge: $1.106 × 730 = $807 + $100 = $907/mo. Recommendation: not_recommended — serverless is ~41% more at this steady load.

5. Memory advisory: your 12 GiB working set means min_ACU MUST be ≥ 6.0 to keep the hot set in memory. min_ACU=8 already satisfies this. If you set min below 6 you will see buffer-cache misses.

6. Migration approaches:

   • In-place (modify-db-cluster --serverless-v2-scaling-configuration): simplest, fastest; brief restart per instance. Caveats: cluster must already be r6+ generation.
   • Blue/Green (recommended for production): new Aurora serverless writer built as green environment, tested under live replication, switchover in <1 min. Best rollback path.
   • Snapshot restore to a new cluster: full rebuild; longest, but gives you a parallel cluster to test end-to-end.

7. Parameter group: MUST be an Aurora serverless-compatible parameter group (family aurora-mysql8.0). DO NOT hardcode innodb_buffer_pool_size (Aurora resizes it with ACU) or max_connections (Aurora derives it from the cluster's maximum ACU; it is static and needs a reboot to change). Override only for well-understood special cases.

8. CloudFormation snippet (Aurora serverless writer):

   ClusterParameterGroup:
     Type: AWS::RDS::DBClusterParameterGroup
     Properties:
       Family: aurora-mysql8.0
       Description: Enforce TLS for Aurora serverless cluster
       Parameters:
         require_secure_transport: "ON"
   DBCluster:
     Type: AWS::RDS::DBCluster
     Properties:
       Engine: aurora-mysql
       EngineVersion: "8.0.mysql_aurora.3.08.0"
       DBClusterParameterGroupName: !Ref ClusterParameterGroup
       ServerlessV2ScalingConfiguration:
         MinCapacity: 8.0
         MaxCapacity: 27.5
       StorageEncrypted: true
       EnableCloudwatchLogsExports:
         - error
         - slowquery
         - audit
   WriterInstance:
     Type: AWS::RDS::DBInstance
     Properties:
       DBInstanceClass: db.serverless
       Engine: aurora-mysql
       DBClusterIdentifier: !Ref DBCluster

9. CDK snippet (TypeScript):

   const parameterGroup = new rds.ParameterGroup(this, "PG", {
     engine: rds.DatabaseClusterEngine.auroraMysql({ version: rds.AuroraMysqlEngineVersion.VER_3_08_0 }),
     parameters: { "require_secure_transport": "ON" },
   });
   const cluster = new rds.DatabaseCluster(this, "Cluster", {
     engine: rds.DatabaseClusterEngine.auroraMysql({ version: rds.AuroraMysqlEngineVersion.VER_3_08_0 }),
     parameterGroup,
     serverlessV2MinCapacity: 8.0,
     serverlessV2MaxCapacity: 27.5,
     writer: rds.ClusterInstance.serverlessV2("Writer"),
     storageEncrypted: true,
     cloudwatchLogsExports: ["error", "slowquery", "audit"],
   });

10. Testing: snapshot-restore to a test cluster first; run full load tests at peak TPS; observe ServerlessDatabaseCapacity CloudWatch metric to verify ACU actually scales with load.

Scale-to-zero / auto-pause rules

Aurora serverless auto-pause requires MinCapacity: 0 and is incompatible with: RDS Proxy, binary logging (binlog) enabled, Global Database primary, and Zero-ETL integrations. If the user's workload has any of these, you MUST warn them that scale-to-zero cannot be enabled, and instead recommend a non-zero MinCapacity (e.g. 0.5 for dev/test, ≥1.0 for prod). In a multi-AZ cluster, auto-pause still works: the writer and any reader instances with failover priority 0 or 1 pause and resume together (their capacity is tied to the writer), while reader instances with failover priority 2-15 can pause independently. So a reader configured with priority 0/1 will not pause unless the writer also pauses — but the cluster as a whole can still scale to zero. See concepts.md for the complete compatibility matrix.