AWS CloudWatch Cross-Account Logging with EC2 Instance Profile - amazon-web-services

Question

When I originally setup CloudWatch, I created an EC2 Instance Profile to automatically grant access to write to the account's own CloudWatch service. Now, I would like to consolidate the logs from several accounts into a central account.
I'd like to implement a simplified architecture that is based on Centralized Logging on AWS. However, these logs will feed an on-premise ELK stack, so I'm only trying to implement the components outlined in red. I would like to solve this without the use of Kinesis.
Either the CloudWatch Agent (CWAgent) doesn't support assuming a role or I can't wrap my mind around how to craft the EC2 Instance Profile to allow the CWAgent to assume a role in a different account.
Logging Target (AWS Account 111111111111)
IAM LogStreamerRole:
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": {
"AWS": [
"arn:aws:iam::999999999999:role/EC2CloudWatchLoggerRole"
]
},
"Action": "sts:AssumeRole",
"Condition": {}
}
]
}
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "",
"Effect": "Allow",
"Action": [
"logs:CreateLogGroup",
"logs:CreateLogStream",
"logs:PutLogEvents"
],
"Resource": [
"arn:aws:logs:*:*:*"
]
}
]
}
Logging Source (AWS Account 999999999999)
IAM Instance Profile Role:
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Principal": {
"Service": "ec2.amazonaws.com"
},
"Action": "sts:AssumeRole"
}
]
}
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "",
"Effect": "Allow",
"Action": "sts:AssumeRole",
"Resource": "arn:aws:iam::111111111111:role/LogStreamerRole"
}
]
}
The CWAgent is producing the following error:
/opt/aws/amazon-cloudwatch-agent/logs/amazon-cloudwatch-agent.log:
2018-02-12T23:27:43Z E! CreateLogStream / CreateLogGroup with log group name Linux/var/log/messages stream name i-123456789abcdef has errors. Will retry the request: AccessDeniedException: User: arn:aws:sts::999999999999:assumed-role/EC2CloudWatchLoggerRole/i-123456789abcdef is not authorized to perform: logs:CreateLogStream on resource: arn:aws:logs:us-west-2:999999999999:log-group:Linux/var/log/messages:log-stream:i-123456789abcdef
status code: 400, request id: 53271811-1234-11e8-afe1-a3c56071215e
It is still trying to write to its own CloudWatch service, instead of to the central CloudWatch service.

Answer 1

From the logs, I see that the instance profile is used.
arn:aws:sts::999999999999:assumed-role/EC2CloudWatchLoggerRole/i-123456789abcdef
Just add the following to the /etc/awslogs/awscli.conf to assume the LogStreamerRole role.
role_arn = arn:aws:iam::111111111111:role/LogStreamerRole
credential_source=Ec2InstanceMetadata