Route table changes alarm remediation

Using Console

Below are step‑by‑step instructions (AWS Console only) to create a CloudWatch alarm for route table changes using CloudTrail logs.

Prerequisites

CloudTrail must be enabled and logging management events (at least Write events) for EC2.
CloudTrail must be delivering logs to a CloudWatch Logs log group.
- If not configured, in the CloudTrail console → Trails → your trail → Edit → CloudWatch Logs and attach/create a log group and an IAM role.

Step 1: Identify/Create the CloudTrail Log Group

Open CloudTrail console.
In the left menu, select Trails.
Click your active trail.
Scroll to CloudWatch Logs section:
- Note the CloudWatch Logs log group name.
- If none is configured, enable it:
  - Click Edit.
  - Under CloudWatch Logs, choose or create a log group (e.g., /aws/cloudtrail/management).
  - Choose/create an IAM role as prompted.
  - Save.

Step 2: Create a Metric Filter for Route Table Changes

Open CloudWatch console.
In the left menu, select Logs → Log groups.
Click the CloudTrail log group you identified (e.g., /aws/cloudtrail/management).
Go to the Metric filters tab.
Click Create metric filter.

In Filter pattern, use a pattern that matches route-table–related API calls, for example:

{ ($.eventSource = "ec2.amazonaws.com") && 
  (
    ($.eventName = "CreateRoute") ||
    ($.eventName = "CreateRouteTable") ||
    ($.eventName = "ReplaceRoute") ||
    ($.eventName = "ReplaceRouteTableAssociation") ||
    ($.eventName = "DeleteRoute") ||
    ($.eventName = "DeleteRouteTable") ||
    ($.eventName = "DisassociateRouteTable")
  )
}

Click Next.
For Filter name, enter something like:
RouteTableChangesFilter
Under Metric details:
- Metric namespace: e.g., Security/NetworkChanges
- Metric name: e.g., RouteTableChanges
- Metric value: 1
- Default value: leave blank or 0.
Click Next, then Create metric filter.

Step 3: Create a CloudWatch Alarm on That Metric

After creating the filter, you’ll see it listed.
Select the filter and click Create alarm (or go to CloudWatch → Alarms → All alarms → Create alarm and select the metric you just created:
Security/NetworkChanges → RouteTableChanges).
In the Specify metric and conditions step:
- Statistic: Sum
- Period: e.g., 5 minutes
- Threshold type: Static
- Condition:
  - Greater than
  - Threshold value: 0
- This means: alarm if at least one route table change occurs in 5 minutes.
Click Next.

Step 4: Configure Alarm Notifications

In Configure actions:
- Alarm state trigger: In alarm
- Under Notification, choose an SNS topic to send alerts to:
  - Select an existing topic (e.g., security-alerts), or
  - Click Create new topic, provide:
    - Topic name: e.g., route-table-changes-alerts
    - Email endpoint(s) (security, ops, etc.).
- Confirm email subscription(s) if prompted.
(Optional) Add additional actions (e.g., OpsCenter, EC2 action – normally not needed here).
Click Next.

Step 5: Name and Create the Alarm

Provide:
- Alarm name: RouteTableChangesAlarm
- Alarm description: e.g., Alerts on any changes to VPC route tables using CloudTrail events.
Review all settings.
Click Create alarm.

Step 6: Test the Alarm (Optional but Recommended)

Make a test route table change (e.g., add a non-impactful route in a test VPC and remove it).
Wait for the metric to update (typically a few minutes).
Confirm:
- Alarm transitions to ALARM state.
- Notification (email/SNS) is received.

This completes enabling a CloudWatch alarm for route table changes using the AWS Console.

Using CLI

Below is a minimal, end‑to‑end way to enable an alarm for Route Table changes in AWS using the AWS CLI.Assumptions:

You already have a CloudTrail trail sending events to a CloudWatch Logs log group (if not, steps 1–2 cover it).
Replace all placeholder values (e.g., MY_TRAIL, my-log-group, my-route-table-changes-metric, my-route-table-changes-alarm, etc.) with your own.

1. (If needed) Configure CloudTrail to send logs to CloudWatch Logs

# 1.1 Create a log group for CloudTrail if you don’t have one
aws logs create-log-group --log-group-name /aws/cloudtrail/management

# 1.2 Attach a role/policy for CloudTrail to write to CloudWatch Logs
# Create an IAM role and policy separately (if not already present).
# Example role name: CloudTrail_CloudWatchLogs_Role

# 1.3 Update / create the trail to send logs to CloudWatch Logs
aws cloudtrail update-trail \
  --name MY_TRAIL \
  --cloud-watch-logs-log-group-arn arn:aws:logs:REGION:ACCOUNT_ID:log-group:/aws/cloudtrail/management \
  --cloud-watch-logs-role-arn arn:aws:iam::ACCOUNT_ID:role/CloudTrail_CloudWatchLogs_Role

2. Create a CloudWatch Logs Metric Filter for Route Table changes

The filter will match API calls that modify Route Tables:

CreateRouteTable
DeleteRouteTable
AssociateRouteTable
DisassociateRouteTable
ReplaceRouteTableAssociation
ReplaceRouteTableRoute
CreateRoute
DeleteRoute
ReplaceRoute

aws logs put-metric-filter \
  --log-group-name /aws/cloudtrail/management \
  --filter-name route-table-changes-filter \
  --filter-pattern '{ ($.eventName = "CreateRouteTable") || ($.eventName = "DeleteRouteTable") || ($.eventName = "AssociateRouteTable") || ($.eventName = "DisassociateRouteTable") || ($.eventName = "ReplaceRouteTableAssociation") || ($.eventName = "ReplaceRouteTableRoute") || ($.eventName = "CreateRoute") || ($.eventName = "DeleteRoute") || ($.eventName = "ReplaceRoute") }' \
  --metric-transformations \
      metricName=my-route-table-changes-metric,metricNamespace=Security,metricValue=1

This will emit a metric Security/my-route-table-changes-metric with value 1 for every matched event.

aws sns create-topic --name route-table-changes-topic

# Capture the TopicArn from the output, e.g.:
# arn:aws:sns:REGION:ACCOUNT_ID:route-table-changes-topic

# Optionally subscribe an email
aws sns subscribe \
  --topic-arn arn:aws:sns:REGION:ACCOUNT_ID:route-table-changes-topic \
  --protocol email \
  --notification-endpoint you@example.com

4. Create a CloudWatch Alarm on the metric

Alarm if at least 1 route table change occurs in a 5-minute period:

aws cloudwatch put-metric-alarm \
  --alarm-name my-route-table-changes-alarm \
  --alarm-description "Alarm when VPC Route Tables are changed" \
  --metric-name my-route-table-changes-metric \
  --namespace Security \
  --statistic Sum \
  --period 300 \
  --threshold 1 \
  --comparison-operator GreaterThanOrEqualToThreshold \
  --evaluation-periods 1 \
  --alarm-actions arn:aws:sns:REGION:ACCOUNT_ID:route-table-changes-topic \
  --treat-missing-data notBreaching

Once done:

Any change to Route Tables (via the listed API calls) will be logged by CloudTrail into the log group.
The metric filter will emit a metric per event.
The CloudWatch alarm will trigger and send a notification via SNS whenever at least one change is detected in the evaluation period.

Using Python

Below is one straightforward way to remediate this in AWS using Python/boto3:Goal:

Detect route table changes via CloudTrail
Send them to CloudWatch Logs
Use a metric filter and CloudWatch Alarm to trigger notifications (e.g., via SNS)

Assumptions:

You have AWS credentials configured.
You have boto3 installed.
You have (or will create) an SNS topic and subscription for notifications.

1. Enable/Verify CloudTrail With CloudWatch Logs

CloudTrail must log management events and send them to a CloudWatch Logs log group.

import boto3

region = "us-east-1"
trail_name = "org-route-table-changes-trail"
log_group_name = "/aws/cloudtrail/route-table-changes"

logs = boto3.client("logs", region_name=region)
ct = boto3.client("cloudtrail", region_name=region)

# 1a. Create log group if it doesn't exist
def ensure_log_group():
    try:
        logs.create_log_group(logGroupName=log_group_name)
    except logs.exceptions.ResourceAlreadyExistsException:
        pass

# 1b. Create or update a trail that sends logs to CloudWatch Logs
def ensure_trail():
    # Replace with an existing S3 bucket used for CloudTrail
    s3_bucket_name = "my-cloudtrail-logs-bucket"

    # Create or update trail
    trails = ct.describe_trails(trailNameList=[trail_name])["trailList"]
    if not trails:
        ct.create_trail(
            Name=trail_name,
            S3BucketName=s3_bucket_name,
            IsMultiRegionTrail=True,
            IncludeGlobalServiceEvents=True,
            IsOrganizationTrail=False,
            CloudWatchLogsLogGroupArn=f"arn:aws:logs:{region}:YOUR_ACCOUNT_ID:log-group:{log_group_name}",
            CloudWatchLogsRoleArn="arn:aws:iam::YOUR_ACCOUNT_ID:role/CloudTrail_CloudWatchLogs_Role",
        )
    else:
        ct.update_trail(
            Name=trail_name,
            CloudWatchLogsLogGroupArn=f"arn:aws:logs:{region}:YOUR_ACCOUNT_ID:log-group:{log_group_name}",
            CloudWatchLogsRoleArn="arn:aws:iam::YOUR_ACCOUNT_ID:role/CloudTrail_CloudWatchLogs_Role",
        )

    # Ensure logging is on
    ct.start_logging(Name=trail_name)


ensure_log_group()
ensure_trail()

Notes:

You must have an IAM role (CloudTrail_CloudWatchLogs_Role) with the proper trust and permissions for CloudTrail → CloudWatch Logs.
Replace YOUR_ACCOUNT_ID, bucket name, role ARN as needed.

2. Create a Metric Filter for Route Table Changes

Filter CloudTrail events for route-table–related eventNames on EC2.Common relevant events:

CreateRoute, DeleteRoute, ReplaceRoute
CreateRouteTable, DeleteRouteTable
AssociateRouteTable, DisassociateRouteTable, ReplaceRouteTableAssociation

metric_filter_name = "RouteTableChangesFilter"
metric_namespace = "SecurityMonitoring"
metric_name = "RouteTableChangeCount"

filter_pattern = """
{ ($.eventSource = "ec2.amazonaws.com") &&
  (
    $.eventName = "CreateRoute" ||
    $.eventName = "DeleteRoute" ||
    $.eventName = "ReplaceRoute" ||
    $.eventName = "CreateRouteTable" ||
    $.eventName = "DeleteRouteTable" ||
    $.eventName = "AssociateRouteTable" ||
    $.eventName = "DisassociateRouteTable" ||
    $.eventName = "ReplaceRouteTableAssociation"
  )
}
"""

logs.put_metric_filter(
    logGroupName=log_group_name,
    filterName=metric_filter_name,
    filterPattern=filter_pattern.strip(),
    metricTransformations=[
        {
            "metricName": metric_name,
            "metricNamespace": metric_namespace,
            "metricValue": "1",
        }
    ],
)

sns = boto3.client("sns", region_name=region)
topic_name = "route-table-changes-topic"

topic_arn = sns.create_topic(Name=topic_name)["TopicArn"]

# Optionally subscribe an email
sns.subscribe(
    TopicArn=topic_arn,
    Protocol="email",
    Endpoint="security-team@example.com",
)
print("Confirm the email subscription from your inbox.")

4. Create a CloudWatch Alarm on the Metric

Alarm when at least 1 route table change occurs in a 5-minute period.

cw = boto3.client("cloudwatch", region_name=region)

alarm_name = "RouteTableChangesAlarm"

cw.put_metric_alarm(
    AlarmName=alarm_name,
    AlarmDescription="Alarm when any VPC route table is modified.",
    Namespace=metric_namespace,
    MetricName=metric_name,
    Statistic="Sum",
    Period=300,  # 5 minutes
    EvaluationPeriods=1,
    Threshold=1.0,
    ComparisonOperator="GreaterThanOrEqualToThreshold",
    TreatMissingData="notBreaching",
    AlarmActions=[topic_arn],
)

5. Validate

Make a test change to a route table.
Wait a few minutes.
Verify:
- CloudTrail shows the event.
- Metric in CloudWatch (SecurityMonitoring/RouteTableChangeCount) increments.
- Alarm transitions to ALARM and sends an SNS notification.

This configuration ensures “Route Table Changes Alarm” is enabled via CloudWatch and fully managed by Python/boto3.

Using Terraform

# CloudWatch Logs metric filter for route table changes
resource "aws_cloudwatch_log_metric_filter" "route_table_changes" {
  name           = "RouteTableChangesFilter"
  log_group_name = "CLOUDTRAIL_LOG_GROUP_NAME" # replace with your CloudTrail log group name

  pattern = "{ ($.eventName = CreateRoute) || ($.eventName = CreateRouteTable) || ($.eventName = ReplaceRoute) || ($.eventName = ReplaceRouteTableAssociation) || ($.eventName = DeleteRouteTable) || ($.eventName = DeleteRoute) || ($.eventName = DisassociateRouteTable) }"

  metric_transformation {
    name      = "RouteTableChangesMetric"
    namespace = "CloudTrailMetrics"
    value     = "1"
  }
}

# Optional: SNS topic for alarm notifications (or use an existing one)
resource "aws_sns_topic" "route_table_changes_notifications" {
  name = "RouteTableChangeNotifications"
}

# CloudWatch alarm for the route table changes metric
resource "aws_cloudwatch_metric_alarm" "route_table_changes" {
  alarm_name          = "RouteTableChangesAlarm"
  alarm_description   = "Monitors for route table changes"
  namespace           = "CloudTrailMetrics"
  metric_name         = "RouteTableChangesMetric"
  statistic           = "Sum"
  period              = 300
  evaluation_periods  = 1
  threshold           = 1
  comparison_operator = "GreaterThanOrEqualToThreshold"

  alarm_actions = [
    aws_sns_topic.route_table_changes_notifications.arn
    # or replace with an existing SNS topic ARN:
    # "ROUTE_TABLE_CHANGES_ALARM_SNS_TOPIC_ARN"
  ]

  depends_on = [aws_cloudwatch_log_metric_filter.route_table_changes]
}

This change will create (or, if the same names already exist and are imported, update) the metric filter RouteTableChangesFilter and alarm RouteTableChangesAlarm; if they are currently unmanaged by Terraform, importing or replacing them may overwrite existing settings. After adding this, terraform plan should show one aws_cloudwatch_log_metric_filter and one aws_cloudwatch_metric_alarm (and optionally aws_sns_topic) to be created or updated with the exact pattern, metric, and threshold described above.

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Route table changes alarm remediation

Triage and Remediation

Remediation

Prerequisites

Step 1: Identify/Create the CloudTrail Log Group

Step 2: Create a Metric Filter for Route Table Changes

Step 3: Create a CloudWatch Alarm on That Metric

Step 4: Configure Alarm Notifications

Step 5: Name and Create the Alarm

Step 6: Test the Alarm (Optional but Recommended)

1. (If needed) Configure CloudTrail to send logs to CloudWatch Logs

2. Create a CloudWatch Logs Metric Filter for Route Table changes

4. Create a CloudWatch Alarm on the metric

1. Enable/Verify CloudTrail With CloudWatch Logs

2. Create a Metric Filter for Route Table Changes

4. Create a CloudWatch Alarm on the Metric

5. Validate

​Triage and Remediation

​Remediation

​Prerequisites

​Step 1: Identify/Create the CloudTrail Log Group

​Step 2: Create a Metric Filter for Route Table Changes

​Step 3: Create a CloudWatch Alarm on That Metric

​Step 4: Configure Alarm Notifications

​Step 5: Name and Create the Alarm

​Step 6: Test the Alarm (Optional but Recommended)

​1. (If needed) Configure CloudTrail to send logs to CloudWatch Logs

​2. Create a CloudWatch Logs Metric Filter for Route Table changes

​3. Create an SNS topic for notifications (if you don’t have one)

​4. Create a CloudWatch Alarm on the metric

​1. Enable/Verify CloudTrail With CloudWatch Logs

​2. Create a Metric Filter for Route Table Changes

​3. Create an SNS Topic (If Needed)

​4. Create a CloudWatch Alarm on the Metric

​5. Validate

Triage and Remediation

Remediation

Prerequisites

Step 1: Identify/Create the CloudTrail Log Group

Step 2: Create a Metric Filter for Route Table Changes

Step 3: Create a CloudWatch Alarm on That Metric

Step 4: Configure Alarm Notifications

Step 5: Name and Create the Alarm

Step 6: Test the Alarm (Optional but Recommended)

1. (If needed) Configure CloudTrail to send logs to CloudWatch Logs

2. Create a CloudWatch Logs Metric Filter for Route Table changes

3. Create an SNS topic for notifications (if you don’t have one)

4. Create a CloudWatch Alarm on the metric

1. Enable/Verify CloudTrail With CloudWatch Logs

2. Create a Metric Filter for Route Table Changes

3. Create an SNS Topic (If Needed)

4. Create a CloudWatch Alarm on the Metric

5. Validate