Centralized logging is often required in large enterprise environments for a number of reasons, ranging from compliance and security to analytics and application-specific needs.

I’ve seen that in a multi-account environment, whether the accounts belong to the same line of business or multiple business units, collecting logs in a central, dedicated logging account is an established best practice. It helps security teams detect malicious activities both in real-time and during incident response. It provides protection to log data in case it is accidentally or intentionally deleted. It also helps application teams correlate and analyze log data across multiple application tiers.

This blog post provides a solution and building blocks to stream Amazon CloudWatch log data across accounts. In a multi-account environment this repeatable solution could be deployed multiple times to stream all relevant Amazon CloudWatch log data from all accounts to a centralized logging account.

Solution Summary 

The solution uses Amazon Kinesis Data Streams and a log destination to set up an endpoint in the logging account to receive streamed logs and uses Amazon Kinesis Data Firehose to deliver log data to the Amazon Simple Storage Solution (S3) bucket. Application accounts will subscribe to stream all (or part) of their Amazon CloudWatch logs to a defined destination in the logging account via subscription filters.

Below is a diagram illustrating how the various services work together.

log destination 1
In logging an account, a Kinesis Data Stream is created to receive streamed log data and a log destination is created to facilitate remote streaming, configured to use the Kinesis Data Stream as its target.

The Amazon Kinesis Data Firehose stream is created to deliver log data from the data stream to S3. The delivery stream uses a generic AWS Lambda function for data validation and transformation.

In each application account, a subscription filter is created between each Amazon CloudWatch log group and the destination created for this log group in the logging account.

The following steps are involved in setting up the central-logging solution:

  1. Create an Amazon S3 bucket for your central logging in the logging account
  2. Create an AWS Lambda function for log data transformation and decoding in logging account
  3. Create a central logging stack as a logging-account destination ready to receive streamed logs and deliver them to S3
  4. Create a subscription in application accounts to deliver logs from a specific CloudWatch log group to the logging account destination
  5. Create Amazon Athena tables to query and analyze log data in your logging account

Creating a log destination in your logging account

In this section, we will setup the logging account side of the solution, providing detail on the list above. The example I use is for the us-east-1 region, however any region where required services are available could be used.

It’s important to note that your logging-account destination and application-account subscription must be in the same region. You can deploy the solution multiple times to create destinations in all required regions if application accounts use multiple regions.

Step 1: Create an S3 bucket

Use the CloudFormation template below to create S3 bucket in logging account. This template also configures the bucket to archive log data to Glacier after 60 days.

{ "AWSTemplateFormatVersion":"2010-09-09", "Description": "CF Template to create S3 bucket for central logging", "Parameters":{ "BucketName":{ "Type":"String", "Default":"", "Description":"Central logging bucket name" } }, "Resources":{ "CentralLoggingBucket" : { "Type" : "AWS::S3::Bucket", "Properties" : { "BucketName" : {"Ref": "BucketName"}, "LifecycleConfiguration": { "Rules": [ { "Id": "ArchiveToGlacier", "Prefix": "", "Status": "Enabled", "Transitions":[{ "TransitionInDays": "60", "StorageClass": "GLACIER" }] } ] } } } }, "Outputs":{ "CentralLogBucket":{ "Description" : "Central log bucket", "Value" : {"Ref": "BucketName"} , "Export" : { "Name" : "CentralLogBucketName"} } }

To create your central-logging bucket do the following:

  1. Save the template file to your local developer machine as “central-log-bucket.json”
  2. From the CloudFormation console, select “create new stack” and import the file “central-log-bucket.json”
  3. Fill in the parameters and complete stack creation steps (as indicated in the screenshot below)
  4. Verify the bucket has been created successfully and take a note of the bucket name

logging details

Step 2: Create data processing Lambda function

Use the template below to create a Lambda function in your logging account that will be used by Amazon Firehose for data transformation during the delivery process to S3. This function is based on the AWS Lambda kinesis-firehose-cloudwatch-logs-processor blueprint.

The function could be created manually from the blueprint or using the cloudformation template below. To find the blueprint navigate to Lambda -> Create -> Function -> Blueprints

lambda function

This function will unzip the event message, parse it and verify that it is a valid CloudWatch log event. Additional processing can be added if needed. As this function is generic, it could be reused by all log-delivery streams.

{ "AWSTemplateFormatVersion":"2010-09-09", "Description": "Create cloudwatch data processing lambda function", "Resources":{ "LambdaRole": { "Type": "AWS::IAM::Role", "Properties": { "AssumeRolePolicyDocument": { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Principal": { "Service": "lambda.amazonaws.com" }, "Action": "sts:AssumeRole" } ] }, "Path": "/", "Policies": [ { "PolicyName": "firehoseCloudWatchDataProcessing", "PolicyDocument": { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "logs:CreateLogGroup", "logs:CreateLogStream", "logs:PutLogEvents" ], "Resource": "arn:aws:logs:*:*:*" } ] } } ] } }, "FirehoseDataProcessingFunction": { "Type": "AWS::Lambda::Function", "Properties": { "Handler": "index.handler", "Role": {"Fn::GetAtt": ["LambdaRole","Arn"]}, "Description": "Firehose cloudwatch data processing", "Code": { "ZipFile" : { "Fn::Join" : ["\n", [ "'use strict';", "const zlib = require('zlib');", "function transformLogEvent(logEvent) {", " return Promise.resolve(`${logEvent.message}\n`);", "}", "exports.handler = (event, context, callback) => {", " Promise.all(event.records.map(r => {", " const buffer = new Buffer(r.data, 'base64');", " const decompressed = zlib.gunzipSync(buffer);", " const data = JSON.parse(decompressed);", " if (data.messageType !== 'DATA_MESSAGE') {", " return Promise.resolve({", " recordId: r.recordId,", " result: 'ProcessingFailed',", " });", " } else {", " const promises = data.logEvents.map(transformLogEvent);", " return Promise.all(promises).then(transformed => {", " const payload = transformed.reduce((a, v) => a + v, '');", " const encoded = new Buffer(payload).toString('base64');", " console.log('---------------payloadv2:'+JSON.stringify(payload, null, 2));", " return {", " recordId: r.recordId,", " result: 'Ok',", " data: encoded,", " };", " });", " }", " })).then(recs => callback(null, { records: recs }));", "};" ]]} }, "Runtime": "nodejs8.10", "Timeout": "60" } } }, "Outputs":{ "Function" : { "Description": "Function ARN", "Value": {"Fn::GetAtt": ["FirehoseDataProcessingFunction","Arn"]}, "Export" : { "Name" : {"Fn::Sub": "${AWS::StackName}-Function" }} } }

To create the function follow the steps below:

  1. Save the template file as “central-logging-lambda.json”
  2. Login to logging account and, from the CloudFormation console, select “create new stack”
  3. Import the file “central-logging-lambda.json” and click next
  4. Follow the steps to create the stack and verify successful creation
  5. Take a note of Lambda function arn from the output section

logging lambda 2 line

Step 3: Create log destination in logging account

Log destination is used as the target of a subscription from application accounts, log destination can be shared between multiple subscriptions however according to the architecture suggested in this solution all logs streamed to the same destination will be stored in the same S3 location, if you would like to store log data in different hierarchy or in a completely different bucket you need to create separate destinations.

As noted previously, your destination and subscription have to be in the same region

Use the template below to create destination stack in logging account.

{ "AWSTemplateFormatVersion":"2010-09-09", "Description": "Create log destination and required resources", "Parameters":{ "LogBucketName":{ "Type":"String", "Default":"central-log-do-not-delete", "Description":"Destination logging bucket" }, "LogS3Location":{ "Type":"String", "Default":"<BU>/<ENV>/<SOURCE_ACCOUNT>/<LOG_TYPE>/", "Description":"S3 location for the logs streamed to this destination; example marketing/prod/999999999999/flow-logs/" }, "ProcessingLambdaARN":{ "Type":"String", "Default":"", "Description":"CloudWatch logs data processing function" }, "SourceAccount":{ "Type":"String", "Default":"", "Description":"Source application account number" } }, "Resources":{ "MyStream": { "Type": "AWS::Kinesis::Stream", "Properties": { "Name": {"Fn::Join" : [ "", [{ "Ref" : "AWS::StackName" },"-Stream"] ]}, "RetentionPeriodHours" : 48, "ShardCount": 1, "Tags": [ { "Key": "Solution", "Value": "CentralLogging" } ] } }, "LogRole" : { "Type" : "AWS::IAM::Role", "Properties" : { "AssumeRolePolicyDocument" : { "Statement" : [ { "Effect" : "Allow", "Principal" : { "Service" : [ {"Fn::Join": [ "", [ "logs.", { "Ref": "AWS::Region" }, ".amazonaws.com" ] ]} ] }, "Action" : [ "sts:AssumeRole" ] } ] }, "Path" : "/service-role/" } }, "LogRolePolicy" : { "Type" : "AWS::IAM::Policy", "Properties" : { "PolicyName" : {"Fn::Join" : [ "", [{ "Ref" : "AWS::StackName" },"-LogPolicy"] ]}, "PolicyDocument" : { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": ["kinesis:PutRecord"], "Resource": [{ "Fn::GetAtt" : ["MyStream", "Arn"] }] }, { "Effect": "Allow", "Action": ["iam:PassRole"], "Resource": [{ "Fn::GetAtt" : ["LogRole", "Arn"] }] } ] }, "Roles" : [ { "Ref" : "LogRole" } ] } }, "LogDestination" : { "Type" : "AWS::Logs::Destination", "DependsOn" : ["MyStream","LogRole","LogRolePolicy"], "Properties" : { "DestinationName": {"Fn::Join" : [ "", [{ "Ref" : "AWS::StackName" },"-Destination"] ]}, "RoleArn": { "Fn::GetAtt" : ["LogRole", "Arn"] }, "TargetArn": { "Fn::GetAtt" : ["MyStream", "Arn"] }, "DestinationPolicy": { "Fn::Join" : ["",[ "{\"Version\" : \"2012-10-17\",\"Statement\" : [{\"Effect\" : \"Allow\",", " \"Principal\" : {\"AWS\" : \"", {"Ref":"SourceAccount"} ,"\"},", "\"Action\" : \"logs:PutSubscriptionFilter\",", " \"Resource\" : \"", {"Fn::Join": [ "", [ "arn:aws:logs:", { "Ref": "AWS::Region" }, ":" ,{ "Ref": "AWS::AccountId" }, ":destination:",{ "Ref" : "AWS::StackName" },"-Destination" ] ]} ,"\"}]}" ]]} } }, "S3deliveryStream": { "DependsOn": ["S3deliveryRole", "S3deliveryPolicy"], "Type": "AWS::KinesisFirehose::DeliveryStream", "Properties": { "DeliveryStreamName": {"Fn::Join" : [ "", [{ "Ref" : "AWS::StackName" },"-DeliveryStream"] ]}, "DeliveryStreamType": "KinesisStreamAsSource", "KinesisStreamSourceConfiguration": { "KinesisStreamARN": { "Fn::GetAtt" : ["MyStream", "Arn"] }, "RoleARN": {"Fn::GetAtt" : ["S3deliveryRole", "Arn"] } }, "ExtendedS3DestinationConfiguration": { "BucketARN": {"Fn::Join" : [ "", ["arn:aws:s3:::",{"Ref":"LogBucketName"}] ]}, "BufferingHints": { "IntervalInSeconds": "60", "SizeInMBs": "50" }, "CompressionFormat": "UNCOMPRESSED", "Prefix": {"Ref": "LogS3Location"}, "RoleARN": {"Fn::GetAtt" : ["S3deliveryRole", "Arn"] }, "ProcessingConfiguration" : { "Enabled": "true", "Processors": [ { "Parameters": [ { "ParameterName": "LambdaArn", "ParameterValue": {"Ref":"ProcessingLambdaARN"} }], "Type": "Lambda" }] } } } }, "S3deliveryRole": { "Type": "AWS::IAM::Role", "Properties": { "AssumeRolePolicyDocument": { "Version": "2012-10-17", "Statement": [ { "Sid": "", "Effect": "Allow", "Principal": { "Service": "firehose.amazonaws.com" }, "Action": "sts:AssumeRole", "Condition": { "StringEquals": { "sts:ExternalId": {"Ref":"AWS::AccountId"} } } } ] } } }, "S3deliveryPolicy": { "Type": "AWS::IAM::Policy", "Properties": { "PolicyName": {"Fn::Join" : [ "", [{ "Ref" : "AWS::StackName" },"-FirehosePolicy"] ]}, "PolicyDocument": { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "s3:AbortMultipartUpload", "s3:GetBucketLocation", "s3:GetObject", "s3:ListBucket", "s3:ListBucketMultipartUploads", "s3:PutObject" ], "Resource": [ {"Fn::Join": ["", [ {"Fn::Join" : [ "", ["arn:aws:s3:::",{"Ref":"LogBucketName"}] ]}]]}, {"Fn::Join": ["", [ {"Fn::Join" : [ "", ["arn:aws:s3:::",{"Ref":"LogBucketName"}] ]}, "*"]]} ] }, { "Effect": "Allow", "Action": [ "lambda:InvokeFunction", "lambda:GetFunctionConfiguration", "logs:PutLogEvents", "kinesis:DescribeStream", "kinesis:GetShardIterator", "kinesis:GetRecords", "kms:Decrypt" ], "Resource": "*" } ] }, "Roles": [{"Ref": "S3deliveryRole"}] } } }, "Outputs":{ "Destination" : { "Description": "Destination", "Value": {"Fn::Join": [ "", [ "arn:aws:logs:", { "Ref": "AWS::Region" }, ":" ,{ "Ref": "AWS::AccountId" }, ":destination:",{ "Ref" : "AWS::StackName" },"-Destination" ] ]}, "Export" : { "Name" : {"Fn::Sub": "${AWS::StackName}-Destination" }} } }

To create your log destination and all required resources, follow these steps:

  1. Save your template as “central-logging-destination.json”
  2. Login to your logging account and, from the CloudFormation console, select “create new stack”
  3. Import the file “central-logging-destination.json” and click next
  4. Fill in the parameters to configure the log destination and click Nextdestination
  5. Follow the default steps to create the stack and verify successful creation
    1. Bucket name is the same as in the “create central logging bucket” step
    2. LogS3Location is the directory hierarchy for saving log data that will be delivered to this destination
    3. ProcessingLambdaARN is as created in “create data processing Lambda function” step
    4. SourceAccount is the application account number where the subscription will be created
  6. Take a note of destination ARN as it appears in outputs section.

lamda function 2 1

Step 4: Create the log subscription in your application account

In this section, we will create the subscription filter in one of the application accounts to stream logs from the CloudWatch log group to the log destination that was created in your logging account.

Create log subscription filter

The subscription filter is created between the CloudWatch log group and a destination endpoint. Asubscription could be filtered to send part (or all) of the logs in the log group. For example,you can create a subscription filter to stream only flow logs with status REJECT.

Use the CloudFormation template below to create subscription filter. Subscription filter and log destination must be in the same region.

{ "AWSTemplateFormatVersion":"2010-09-09", "Description": "Create log subscription filter for a specific Log Group", "Parameters":{ "DestinationARN":{ "Type":"String", "Default":"", "Description":"ARN of logs destination" }, "LogGroupName":{ "Type":"String", "Default":"", "Description":"Name of LogGroup to forward logs from" }, "FilterPattern":{ "Type":"String", "Default":"", "Description":"Filter pattern to filter events to be sent to log destination; Leave empty to send all logs" } }, "Resources":{ "SubscriptionFilter" : { "Type" : "AWS::Logs::SubscriptionFilter", "Properties" : { "LogGroupName" : { "Ref" : "LogGroupName" }, "FilterPattern" : { "Ref" : "FilterPattern" }, "DestinationArn" : { "Ref" : "DestinationARN" } } } }

To create a subscription filter for one of CloudWatch log groups in your application account, follow the steps below:

  1. Save the template as “central-logging-subscription.json”
  2. Login to your application account and, from the CloudFormation console, select “create new stack”
  3. Select the file “central-logging-subscription.json” and click next
  4. Fill in the parameters as appropriate to your environment as you did above
    a.  DestinationARN is the value of obtained in “create log destination in logging account” step
    b.  FilterPatterns is the filter value for log data to be streamed to your logging account (leave empty to stream all logs in the selected log group)
    c.  LogGroupName is the log group as it appears under CloudWatch Logs
  5. Verify successful creation of the subscription

This completes the deployment process in both the logging- and application-account side. After a few minutes, log data will be streamed to the central-logging destination defined in your logging account.

Step 5: Analyzing log data

Once log data is centralized, it opens the door to run analytics on the consolidated data for business or security reasons. One of the powerful services that AWS offers is Amazon Athena.

Amazon Athena allows you to query data in S3 using standard SQL.

Follow the steps below to create a simple table and run queries on the flow logs data that has been collected from your application accounts

  1. Login to your logging account and from the Amazon Athena console, use the DDL below in your query  editor to create a new table
CREATE EXTERNAL TABLE IF NOT EXISTS prod_vpc_flow_logs ( Version INT, Account STRING, InterfaceId STRING, SourceAddress STRING, DestinationAddress STRING, SourcePort INT, DestinationPort INT, Protocol INT, Packets INT, Bytes INT, StartTime INT, EndTime INT, Action STRING, LogStatus STRING ) ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.RegexSerDe' WITH SERDEPROPERTIES ( "input.regex" = "^([^ ]+)\\s+([0-9]+)\\s+([^ ]+)\\s+([^ ]+)\\s+([^ ]+)\\s+([^ ]+)\\s+([^ ]+)\\s+([^ ]+)\\s+([^ ]+)\\s+([^ ]+)\\s+([0-9]+)\\s+([0-9]+)\\s+([^ ]+)\\s+([^ ]+)$") LOCATION 's3://central-logging-company-do-not-delete/';

2. Click ”run query” and verify a successful run/ This creates the table “prod_vpc_flow_logs”

3. You can then run queries against the table data as below:

Final 8


By following the steps I’ve outlined, you will build a central logging solution to stream CloudWatch logs from one application account to a central logging account. This solution is repeatable and could be deployed multiple times for multiple accounts and logging requirements.