Why playing with AWS DynamoDb "Hello world" produces read/write alarms?

Question

I'v started to play with DynamoDb and I'v created "dynamo-test" table with hash PK on userid and couple more columns (age, name). Read and write capacity is set to 5. I use Lambda and API Gateway with Node.js. Then I manually performed several API calls through API gateway using similar payload:

{
  "userId" : "222",
   "name" : "Test",
   "age" : 34
 }

I'v tried to insert the same item couple times (which didn't produce error but silently succeeded.) Also, I used DynamoDb console and browsed for inserted items several times (currently there are 2 only). I haven't tracked how many times exactly I did those actions, but that was done completely manually. And then after an hour, I'v noticed 2 alarms in CloudWatch:

INSUFFICIENT_DATA dynamo-test-ReadCapacityUnitsLimit-BasicAlarm ConsumedReadCapacityUnits >= 240 for 12 minutes No notifications

And the similar alarm with "...WriteCapacityLimit...". Write capacity become OK after 2 mins, but then went back again after 10 mins. Anyway, I'm still reading and learning how to plan and monitor these capacities, but this hello world example scared me a bit if I'v exceeded my table's capacity :) Please, point me to the right direction if I'm missing some fundamental part!

Answer 1

It's just an "INSUFFICIENT_DATA" message. It means that your table hasn't had any reads or writes in a while, so there is insufficient data available for the CloudWatch metric. This happens with the CloudWatch alarms for any DynamoDB table that isn't used very often. Nothing to worry about.

EDIT: You can now change a setting in CloudWatch alarms to ignore missing data, which will leave the alarm at its previous state instead of changing it to the "INSUFFICIENT_DATA" state.