CCNA Incident and Event Response Questions

AWS Systems Manager Run Command is part of AWS Systems Manager and lets you remotely and securely execute shell commands or PowerShell scripts on EC2 instances (and on-premises machines) via the SSM Agent. You can run a command like `ps aux` or `Get-Process` to enumerate running processes, capture output, and store it in S3 or CloudWatch Logs. Because the SSM Agent runs inside the instance as a guest process, it has direct access to OS-level state, making it the appropriate service for collecting process-level data. It also supports rate control and error handling for fleet-wide execution.

The ECS service's Application Auto Scaling target tracking policy is capped by a maximum capacity of 10 tasks. Since the service is already running at that desired count of 10, the policy cannot scale out any further even though the CloudWatch metric is above the target value. To resolve the issue, increase the maximum tasks (for example, from 10 to 15) in the scaling configuration, which allows the policy to add more task instances.

To encrypt a CloudWatch Logs log group with a customer-managed KMS key, you must create or select a KMS key, update its key policy to grant the CloudWatch Logs service principal permissions such as kms:Encrypt, kms:Decrypt, kms:GenerateDataKey*, and kms:DescribeKey, and then associate that key with the log group using the console or the associate-kms-key API. This server-side encryption protects log data at rest and allows CloudWatch Logs to decrypt the data internally for features like log queries.

The SSM Agent downloads patch binaries directly from the configured patch repositories, such as Windows Update or Linux package mirrors, using HTTPS on TCP port 443. If the instance's security group or subnet NACL blocks outbound HTTPS, the agent cannot reach these repositories, leading to a patch download failure. This is the most common network-level cause, especially when the instance can otherwise communicate with the Systems Manager API but fails specifically during patch retrieval.

Amazon RDS Performance Insights gives you an at-a-glance dashboard of database load (measured in average active sessions), broken down by wait events, SQL statements, hosts, and users. This allows you to see exactly which query is consuming the most resources and why—whether it is blocked on locks, I/O, or CPU. Its historical and real-time views enable you to pinpoint and correlate the slow query with the performance problem, making it the correct choice for this scenario.

Change Sets generate a preview of proposed resource modifications without applying them, and the manual approval step gates execution until reviewers accept. This satisfies the requirement for review before production changes and blocks unauthorised updates.

AWS WAF rate-based rules track the number of requests from each client IP over a rolling evaluation window (typically 5 minutes) and, when a configured threshold is exceeded, automatically block that IP for a specified duration. This provides immediate, in-place mitigation on the existing ALB without DNS changes, making it the fastest L7 DDoS countermeasure. You can tune the rate limit and scope (e.g., by URI or session) to allow legitimate bursts while dropping attack traffic.

Amazon Simple Notification Service (SNS) is a fully managed pub/sub messaging service that delivers messages to subscribers such as email, SMS, Lambda, or HTTP endpoints. When a CloudWatch alarm transitions to the ALARM state for the StatusCheckFailed metric, it publishes a message to an SNS topic, which then fans out the notification to all subscribed endpoints. This makes SNS the essential delivery mechanism for alerting the DevOps engineer promptly without requiring polling or custom integration code, and it integrates seamlessly with CloudWatch Alarms.

This is the correct first step because CloudWatch provides two directly relevant metrics for an RDS for MySQL instance: DatabaseConnections shows the number of client sessions currently established, and CPUUtilization reflects aggregate CPU consumption. If DatabaseConnections spikes while CPUUtilization remains normal, the problem is connection exhaustion or a connection leak; if CPUUtilization also rises, it likely indicates heavy query load. These metrics give you a high-level, time-aligned picture of whether the symptom is connection-bound or compute-bound, which drives the next diagnostic step (e.g., enabling Performance Insights).

VPC Flow Logs are correct because they capture IP traffic metadata at the elastic network interface level, including source/destination IP addresses, ports, protocol, and the accept/reject action for each flow. This data directly shows which connections were made, from where, and to which destination, enabling a DevOps engineer to trace the communication patterns involved in the incident. These logs can be enabled per VPC, subnet, or ENI and delivered to CloudWatch Logs or S3 for analysis.

Reviewing the instance's CPU credit balance is the correct first step because a T-series instance that exhausts its earned credits will be throttled to the baseline CPU, causing slowdowns even when the alarm threshold is breached. The network utilization metric is also essential since high network throughput can drive CPU overhead from interrupt handling and packet processing, which may be the actual root cause. Together, these metrics reveal whether the alarm reflects genuine resource contention or a misconfigured alarm threshold.

AWS CloudTrail records all IAM user and role API activity as events, including the source IP address, user agent, event name, and whether the call was authorized. Analyzing CloudTrail logs with querying or visualization tools helps you identify which unauthorized or anomalous calls occurred, when they occurred, and what resources were accessed, so you can scope the impact and determine whether other remediation steps are needed. It is the first responder's forensic tool for understanding the security incident.

The default EC2 monitoring only exposes hypervisor-level metrics like CPU, network, and disk I/O; memory utilization is a guest-OS metric that AWS cannot see without an in-guest component. Installing the unified CloudWatch agent (with the `mem_used_percent` and similar metrics in the agent's JSON config) and starting the `amazon-cloudwatch-agent` service enables the agent to publish memory metrics to CloudWatch, making them available for alarms and dashboards. This is required because no amount of instance-level monitoring settings can surface guest-OS memory.

Performance Insights delivers a comprehensive, real-time view of database load, breaking down utilization by waits, SQL statement, and host. By drilling into the 'Top SQL' section, you can pinpoint the exact queries consuming the most CPU, along with statistics such as rows examined and temp tables. This evidence-based approach allows you to optimize indexes or rewrite expensive statements, directly addressing the observed CPU spike.

This is correct because an SQS-triggered Lambda invocation has a maximum execution window set by the function timeout, and the SQS visibility timeout controls when unacknowledged messages become visible again for redelivery. If the function timeout is too short, valid work gets aborted, and if the visibility timeout is shorter than the processing time, the message is re-delivered before the first attempt finishes, causing duplicate work and retries that inflate the backlog. Setting the visibility timeout to 90 seconds (longer than the 60-second function timeout) ensures the message stays hidden until the Lambda function either succeeds or itself times out, giving the function the full time it needs.

AWS Security Hub is the correct answer because it is designed as a multi-account, multi-region aggregation service that centralizes security findings from AWS services and partner products. It enables a delegated administrator to view a consolidated security posture across the entire AWS Organizations hierarchy, evaluate compliance against standards like CIS and NIST, and automate responses via custom actions and AWS Config rules.

HealthyHostCount directly reflects the number of targets that are passing the configured health checks. For a target group with EC2 instances, it is the authoritative CloudWatch metric for monitoring target health; when all instances fail, this value drops to zero, leaving the ALB with no registered and healthy targets to serve traffic, which causes it to return HTTP 503 Service Unavailable. Therefore, it is the correct metric to identify the described incident.

AWS CloudTrail is the authoritative service for auditing API calls, and it natively records Systems Manager management events such as SendCommand, RunCommand, and StartSession. When a trail is enabled (or via the default event history), each event includes the IAM principal, source IP address, event time, request parameters, and response elements, yielding a complete 'who did what' record. This is precisely what is needed to audit and govern SSM usage across an EC2 fleet.

API Gateway imposes a hard 10 MB payload size limit for REST API responses (and 4 MB for HTTP APIs). When a Lambda function returns a response exceeding this threshold, API Gateway cannot process it and returns a 502 Bad Gateway error to the client, with no error logged from the Lambda side because the function already completed successfully. This is the classic 'silent' 502 cause and matches the symptoms in the question.

For a true cross-region disaster recovery, an Amazon RDS read replica in a second region can be promoted to a standalone primary instance during failover. The replica is typically created with asynchronous replication, so some data loss may occur, but it provides a writable database endpoint in the secondary region. This is a standard DR pattern for maintaining business continuity.

The EC2 system log (console output) is a hypervisor-accessible snapshot of the instance's serial port, capturing kernel panics, OOM killer events, and boot-time failures that may be invisible from inside the OS. Pairing that with CloudWatch Logs—where the CloudWatch agent streams Apache, Nginx, or custom application errors—gives you a non-disruptive, evidence-based starting point to pinpoint whether the web service stopped due to memory exhaustion, a crashed process, or an external dependency. These sources are available via the EC2 console or the get-console-output CLI call and require no downtime, making them the correct first step for diagnosis.

The CloudFormation console Events tab lists every operation performed on a stack in chronological order, one per resource action, including statuses like CREATE_FAILED and UPDATE_FAILED. For each failed event, the Status Reason field contains the exact error message returned by the underlying service, such as an IAM permission issue or a missing S3 bucket. This is the authoritative source for diagnosing stack deployment problems.

MemoryUtilization, published as a custom metric by the CloudWatch Agent, is calculated from /proc/meminfo or OS-level memory counters and represents the percentage of actual RAM in use. A memory leak causes this value to climb continuously over time as allocations are never freed, even when the workload is stable. Monitoring this metric reveals the leak as a monotonic upward trend, making it one of the most direct and essential signals for detection.

With session stickiness enabled on the ALB target group, the load balancer consistently routes a given client's requests to the same EC2 instance for the stickiness duration. When a few power users or long-lived connections generate heavy traffic, those specific instances absorb a disproportionate share of load, causing CPU utilization to spike even if the aggregate fleet average remains moderate. This creates a hot-spot pattern where some targets are saturated while others idle, and the Auto Scaling group, if scaling on average CPU, may not react in time.

AWS Config conformance packs provide a way to deploy a collection of AWS Config rules and remediation actions across all accounts and Regions in an organization. A managed rule such as `cloudtrail-enabled` can be included in a conformance pack to verify that CloudTrail trails are configured and enabled, and the results are aggregated centrally in the AWS Config console for the entire organization. This approach gives a single, policy-as-code mechanism to enforce and audit CloudTrail enablement consistently across every account.

VPC Flow Logs capture IP traffic metadata for every network interface in a VPC, subnet, or at the interface level, recording source and destination IP addresses, ports, protocol, packet/byte counts, and whether the action was accepted or rejected by security groups and network ACLs. Enabling flow logs on the affected VPC or subnets would immediately provide the raw data needed to identify the top talkers, unusual port usage, or malicious sources behind the spike. This makes it the correct service for diagnosing an unexpected increase in network traffic.

Deregistering the instance from the Target Group stops new traffic from the Application Load Balancer while leaving the instance running, which preserves volatile memory for forensic collection. Stopping the instance (not terminating it) retains the EBS volumes, allowing investigators to create snapshots or attach them to a forensic workstation for offline analysis. This approach keeps the remaining fleet operational and maintains availability while containing the compromise.

The AWS Config managed rule iam-role-max-session-duration evaluates every IAM role in the account, comparing each role's MaxSessionDuration setting against the rule's maxSessionDuration parameter. This rule is triggered proactively on configuration changes and periodically, so it detects both existing and newly modified roles, flagging any role whose allowed session duration exceeds the defined threshold as noncompliant. It integrates with AWS Organizations and can be remediated automatically or through Config conformance packs.

CloudWatch alarms use the state INSUFFICIENT_DATA when the number of metric data points available in the evaluation period is less than the number required to determine the alarm state. This commonly occurs for a newly created alarm before the first metric points arrive, when an instance is stopped and stops publishing metrics, or when the metric name is missing. The alarm cannot evaluate to ALARM or OK until the metric stream provides enough valid points within the configured period.

The Auto Scaling group’s activity history is the authoritative record of every scale-out and scale-in event, including the time, instance ID, reason code, and status (e.g., 'InProgress', 'Successful', or 'Failed'). By reviewing it, you can determine whether the CloudWatch alarm triggered the scaling policy, whether the capacity was blocked by the maximum instance limit, a service quota, or a launch template error. This directly shows why the instance did not receive the expected scale-out action, making it the correct first troubleshooting step.

This pair provides end-to-end compliance: AWS Config continuously evaluates security group resources against rules like restricted-common-ports, and when an SG is non-compliant, Config's remediation action triggers an AWS Systems Manager Automation runbook (e.g., AWS-DisablePublicSecurityGroupIngress or a custom runbook). The Automation step performs the actual modification, such as revoking offending ingress rules, thus closing the loop. Config can remediate automatically via SSM Automation without manual intervention, making this the correct solution.

This option is correct because when the 'Private DNS names enabled' option is not selected for an Amazon ECR VPC endpoint, the default DNS endpoint (ecr.<region>.amazonaws.com) continues to resolve to public IP addresses. Since the ECS task runs in a private subnet with no internet route, the ECS agent sends the request to a public IP that is unreachable, and the VPC endpoint responds with AccessDenied because the request is not being handled by the endpoint. Enabling private DNS names creates a Route 53 private hosted zone that associates the endpoint's DNS with its private IP, ensuring traffic destined for ECR is routed through the VPC endpoint and bypasses the public network.

Adding an appropriate index transforms a full table scan into an index seek, drastically reducing the number of rows the database engine must read and process, which directly lowers the CPU cycles spent on evaluating rows, join operations, and sort operations. An index that matches the query predicate (e.g., on the columns used in WHERE, JOIN, or ORDER BY) allows the optimizer to access only relevant pages, shrinking buffer pool I/O and improving overall query latency. This is the root-cause fix because it eliminates the unnecessary CPU work rather than merely hiding the symptom.