Reliability and Business Continuity (22%)

SOA-C03 · 66 questions

• A SaaS billing tier's RDS for MySQL instance is CPU-bound by the same product-catalog SELECT statements from many application servers. Results may be a few seconds stale. Which change takes most of those repeated reads off the database?
• A bank runs Amazon RDS for PostgreSQL as a single Availability Zone instance. The database must fail over on its own if that Availability Zone is lost, without an operator promoting a replica. Which configuration meets that requirement?
• A streaming studio keeps a smaller but complete copy of its control plane in a second Region. That copy serves almost no traffic until failover, when the team scales it up. Which disaster recovery pattern is this?
• A university Application Load Balancer marks every target unhealthy, yet a curl of each instance's home page returns HTTP 200. The target group health check uses the path /healthz, and the application does not serve that path. What is the least disruptive fix?
• A hospital web Auto Scaling group stays at four instances while CPU remains above the target tracking policy threshold and pages are timing out. The group's maximum capacity is also four. What should the operator change so the group can add instances?
• A freight carrier takes occasional manual EBS snapshots and has no backup plan for its RDS instances. Leadership wants tagged EBS volumes and RDS instances backed up on a schedule, with a recovery copy in a second Region. Which service should operations configure?
• An Auto Scaling group's activity says there is not enough instance capacity in the single subnet it is allowed to use. The launch template's instance type is acceptable in other Availability Zones. What should change first?
• A payments Auto Scaling group has both a target tracking policy, aimed at holding average CPU near a set point, and a step scaling policy on the same CPU metric. Capacity oscillates all afternoon. The team wants the CPU held near that set point. Which change matches the goal?
• A retailer knows a sale will start at 09:00 and that the web tier must already be scaled out before traffic arrives. Last time, an operator edited desired capacity during the rush and was late. What should they configure beforehand?
• A game studio's Auto Scaling instances stay in Pending:Wait. A lifecycle hook is attached, and the hook's action never calls back. The application on the instance is already healthy. What should the hook do so launching can finish?
• An Auto Scaling group scaled out, and a second CPU alarm fired two minutes later. No further instances launched. The group's cooldown is still running from the first scale-out. The team is about to add another scaling policy on the same metric. What should they do instead?
• A retail Auto Scaling group shows desired capacity above the number of instances in service. Target tracking raised desired capacity, and the activity history is not launching anything. Launch is in the list of suspended processes. What should the operator do?
• Scale-out for a retail Auto Scaling group works, but new instances take several minutes to serve traffic and the warm pool is empty. The team is about to raise only the health-check grace period. What addresses the slow start?
• A Lambda function is throttled during a sale. The account is well under its regional concurrency quota. This function's reserved concurrency is set to 10, and the sale is driving far more concurrent executions than that. What should change?
• An ECS service on EC2 is set to a higher desired count, and the count does not rise. The service maximum percent is 100, and the cluster's container instances have no spare CPU or memory. What is the constraint?
• New instances in an Auto Scaling group fail their health checks within a minute and are replaced, over and over. The application never listens. Raising the maximum was proposed. What should be fixed?
• A university's web tier is busy every weekday at 08:00 and quiet afterward. Last week, target tracking added instances ten minutes after students had already timed out. What should be in place before 08:00?
• An Auto Scaling group uses target tracking on ALBRequestCountPerTarget. Desired capacity never changes, and no targets are registered in the load balancer. The application is not receiving traffic. Why is the policy idle?
• A media company's ElastiCache for Redis catalog is rejecting new writes because the node is at maxmemory and maxmemory-policy is noeviction. Every catalog key can be rebuilt from the database. Which change lets new keys in by dropping cold ones?
• A SaaS API sends every catalog read to the ElastiCache primary endpoint, from instances in another Availability Zone, while replicas in the cache's own zone sit idle. Writes are rare. Which change offloads those reads?
• A retailer's CloudFront distribution is serving one shopper's cart JSON to a different shopper. The behavior caches the API path, and the cache policy does not include the session cookie. Cart responses must not be stored at the edge. What should change?
• ECS tasks stay pending. The service uses a capacity provider backed by an Auto Scaling group, and that group is already at its maximum size. The instances are full. What is the limit?
• A public marketing site serves images and CSS that rarely change. The team is about to cache those files in an ElastiCache node inside one VPC. What reaches viewers at the edge instead?
• A session cache must keep serving after one cache node is lost. The data is in ElastiCache. Memcached was proposed because it is simple. What should they run instead?
• A bank's RDS for PostgreSQL instance is near its CPU limit, and Performance Insights shows the time going to read-only reporting queries. Writes are light. The standby in the Multi-AZ pair does not serve those reads. What should be added?
• A retail inventory table in DynamoDB is provisioned, and the request rate swings without a daily pattern. Throttling shows up on both reads and writes at unpredictable hours. Which capacity mode fits that pattern?
• A logistics table in DynamoDB throttles one popular tracking key while the table's consumed capacity stays well under its provisioned ceiling. Other keys on the table are fine. What should change?
• A retailer caches product prices in ElastiCache with a TTL of several hours. The merchandising rule is that a shopper must not see a price older than a minute. Stale prices are showing on the site well after each update. What should change?
• A game studio stored session tokens only in ElastiCache for Memcached. A node replacement emptied that node and every player on it was signed out. The sessions must survive a node replacement. What should hold them?
• A media company's Aurora writer is at high CPU while its readers sit idle. The busy statements are read-only audience reports, and the application sends those reports to the writer endpoint. Where should the reports connect?
• A game studio's DynamoDB table uses auto scaling, reaches the maximum capacity on that policy during the evening peak, and still returns throttle errors. What should they change?
• Readers of a news site connect through an Application Load Balancer, but the Route 53 health check targets one instance IP. The check stayed healthy while the load balancer failed. What should they change?
• A water utility's Auto Scaling group replaces new instances before the application is listening. The group uses load balancer health checks, and the grace period is shorter than boot. What should they change?
• A city agency's RDS database has storage autoscaling disabled, and free storage is almost gone. They need to act before the instance can stop accepting connections. What should they do?
• A media company's Aurora Serverless v2 writer sits at its minimum capacity while new connections queue, and the cluster minimum and maximum capacity are set to the same value. What should the operator change?
• A logistics company expects its Amazon RDS cross-Region read replica to fail over synchronously, with no lag, when the primary Availability Zone is lost. What does that replica actually provide?
• A hospital target group has its deregistration delay set to zero. Every deploy removes targets while requests are still in flight, and those requests fail. What should change?
• Every instance in an ALB target group stays unhealthy, yet a login on an instance gets a normal response from the application on the health port. The instance security group does not allow the load balancer to reach that port. What should change?
• A ticket seller sees errors only from customers whose session is pinned to one Application Load Balancer target. That target still passes its health check, and the other targets are healthy. What should they change?
• A logistics Route 53 health check fails only because it targets a private address the public checkers cannot reach. The service also has a healthy public endpoint. What should the health check target?
• A logistics Network Load Balancer has cross-zone load balancing turned off. One Availability Zone has no healthy targets, and requests that reach the node in that zone fail while other zones are healthy. What lets that node send work to healthy targets in other zones?
• Players of a game receive errors from a target that the Network Load Balancer still marks healthy. The target group health check is a TCP check on the listener port. What should operators investigate?
• An Auto Scaling group for a clinic portal launches every instance into one subnet in a single Availability Zone. During a zone impairment the whole fleet goes offline. What should be added so the group can launch in the other zones?
• Game clients connect to an Elastic IP associated with one instance. When that Availability Zone fails, an operator must move the address by hand, and the rest of the fleet is unused. What should clients use for failover instead?
• Three private subnets, one in each Availability Zone, send all egress through a single zonal NAT gateway in one zone. If that zone fails, instances in the other zones lose their default route. Keeping zonal NAT gateways, what should change so a surviving zone keeps egress?
• Two Regional checkout endpoints already have Route 53 health checks, but the public name is still one simple record with a fixed address and no health check. DNS keeps answering when both Regions are down. How should that name follow both checks?
• A campus portal stores user sessions as files on one instance disk. When that Availability Zone is lost, new instances have no session and users are signed out. What removes that single-instance session store?
• A library catalog points read-only reports at a hostname the team reserved for the standby of a Multi-AZ RDS DB instance. Those connections never get a database session. Where should the reports read?
• A DBA tested Multi-AZ failover by rebooting the RDS primary from the console without failover selected. The same instance returned as the primary and the standby never took over. Which action tests the standby path?
• An Aurora cluster already stores its data across Availability Zones, and the only database instance is the writer in one zone. Loss of that zone would leave no instance to promote. What should be added?
• Finance policy forbids deleting recovery points before their retention ends. Operators who can use the backup vault can still delete those points today. The vault has no lock. What should be added?
• An AWS Backup plan should protect every volume tagged for the nightly job, but each run reports that no resources were selected. Those volumes use a different tag key than the plan selection. What should be corrected?
• A technician copies EBS snapshots to another Region with a script on a laptop. The copies stop whenever that laptop sleeps or leaves the network. How should the cross-Region copy run instead?
• Point-in-time recovery is turned off on a DynamoDB table. The only recovery copy is a monthly export to S3, and the team must restore to a recent moment between those exports. What should be enabled?
• A ledger application must be able to recover recent writes. Its only backup is a snapshot taken once a day, and that misses the recovery point the application requires. What should change?
• After a point-in-time restore, a new RDS instance is online with a different endpoint. The ticketing application's configuration still names the original endpoint, so it reads the old database. What should change?
• A bank holds an RDS snapshot in one Region and must restore the database in a second Region. The snapshot has not been copied anywhere else. What must exist in the second Region before the restore?
• A city's AWS Backup job cannot snapshot an RDS database. The IAM role AWS Backup uses to take RDS snapshots was never created. What should the operator do?
• An operator restores an RDS snapshot and selects the production database's existing identifier. The restore fails, and the original instance is still running under that name. What should the restore use?
• A clinic needs its patient-records database as it stood about 20 minutes ago. Automated backups are enabled, and the only hand-made copy is last night's manual snapshot. Which restore reaches that time?
• Versioning is enabled on a contracts bucket. A cleanup deleted an object and did not specify a version ID. The console shows the key as deleted, and the older versions are still listed. How is the current view of that key restored?
• In the recovery Region, only the database is running. Application instances are launched from images when a failover is declared, and no scaled-down copy of the application is already serving there. Which disaster-recovery pattern is this?
• The only recovery copy of an application is a nightly backup. Nothing is running at the second site until that backup is restored, and the rebuild takes a full day. The business wants the service back the same morning. Which disaster-recovery pattern is this, and why does it miss that recovery time?
• Two Regions serve this application's production traffic all the time. When one Region is unhealthy, traffic shifts to the other, and nothing has to be launched for that shift. Which disaster-recovery pattern is this?
• A bad push corrupted folders on an Amazon FSx for Windows File Server share. A user-initiated FSx backup from the evening before the push exists, and automatic backups are turned off. One Windows client that maps the share has an EBS snapshot taken this morning. What restores the share?
• An analyst overwrote a pricing object in an S3 bucket that has never had versioning. No backup or replica of that object exists, and the previous contents are required for an audit. What is true about recovery, and what should change before the next overwrite?