Response limit of 4k for CloudFormation Custom Resources

Using the AwsCustomResource construct to easily pass in SDK calls is very useful. Some service calls however have a large response body and lead to Response object is too long. in their CloudFormation response.

It would be nice to have a conditional to check for that and truncate, or more ideally, have a property to control what output goes into the response body, similar to how physicalResourceIdPath works.

[NukaCody]

This shamefully took me 11 attempts to get right so here’s a working example to save others that come across this

    const cr = new AwsCustomResource(this, "EC2InstancePrivateIPv6", {
      onCreate: {
        service: "EC2",
        action: "describeInstances",
        physicalResourceId: PhysicalResourceId.of(`${db.instanceId}-ipv6`),
        parameters: {
          InstanceIds: [db.instanceId],
        },
        outputPaths: ["Reservations.0.Instances.0.NetworkInterfaces.0.Ipv6Addresses.0.Ipv6Address"],
      },
      policy: AwsCustomResourcePolicy.fromSdkCalls({ resources: AwsCustomResourcePolicy.ANY_RESOURCE }),
    });

    const ipv6Address = cr.getResponseField("Reservations.0.Instances.0.NetworkInterfaces.0.Ipv6Addresses.0.Ipv6Address");
    new AaaaRecord(this, "IPv6Record", {
      zone: privateZone,
      recordName: "pg",
      target: RecordTarget.fromIpAddresses(ipv6Address),
    });

It turned out I was assuming the response would be return like an API call Reservations[0].Instances[0]...etc. Double check the lambda logs if you run across the response limit error and see how the data Is outputed

[dacort]

FYI, I ran into a similar error message but it was due to an error in my helm chart where the resulting error message was too big for Lambda to return. Looking at the Lambda logs showed the specific error message.