Pro · Lesson 8 of 11
Validation compares rows. CloudWatch shows whether the task is keeping up. Neither one proves the application is ready.
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Validation is counting the boxes on both docks. CloudWatch is the clock on the truck. A matching count does not mean the shop signs were translated.
Turn validation on for a task when you need DMS to compare source and target rows. It adds load. It does not replace a query you wrote for a table you care about. Mismatches show up as a validation state, not as a green full-load percentage.
Validation will not notice a wrong procedure, a missing index you meant to add later, or an application still pointed at the source.
CloudWatch metrics include full-load throughput and CDC latency on the source and the target. The useful question is whether latency is growing. A task that is "running" with climbing CDC latency is falling behind.
Task logs go to a CloudWatch log group. When a table fails, the log line is more useful than the task's overall percentage. A replication instance that is out of memory or storage fails in those logs and in instance metrics. Serverless tasks have capacity metrics instead of an instance class graph. Read the page for the compute you chose.
| Signal | It means | It does not mean |
|---|---|---|
| Validation failed | Some compared rows differ | Which business rule is wrong |
| CDC latency rising | The target is falling behind the source | That the task has stopped |
| Full load 100% | The load phase finished | That CDC has caught up |
During a migration the source keeps changing, so you check two things: lag and row equality.
Step 1 of 3The application is still writing to the source while DMS copies it, so the target is always catching up.
Source: 1,250 new orders in the last hour
Step 2 of 3CDC latency is how many seconds the target is behind the source. Watch it fall close to zero before you plan a cutover.
CloudWatch → CDCLatencySource / CDCLatencyTarget
Step 3 of 3Data validation compares rows between source and target and reports mismatches. It checks data, not whether the application behaves the same.
Task → Table statistics → Validation state: Validated
Leave the values blank until a real task exists. The list is the habit.
CDC source latency:
CDC target latency:
Validation failures:
Log group:
Table that failed, if any:
Application still on the source: yes/no
Checked against the linked documentation in October 2026. A later release can move a flag, a price, or a supported pair. Use the page for the version you installed.