https://sim.shahriarlabs.com/Free problem guides and interactive comparisonshttps://sim.shahriarlabs.com/guides/ec2-ssh-connection-timed-out/https://sim.shahriarlabs.com/guides/ec2-ssh-connection-timed-out/A timeout means the connection did not complete. Check the instance, public address, subnet route, security group and both NACL directions before changing credentials.https://sim.shahriarlabs.com/guides/private-subnet-no-internet/https://sim.shahriarlabs.com/guides/private-subnet-no-internet/A private instance needs a usable outbound path. For public NAT, verify the private route to NAT, NAT state and VPC, its public subnet route to an attached internet gateway, and both subnet ACLs.https://sim.shahriarlabs.com/guides/s3-access-denied/https://sim.shahriarlabs.com/guides/s3-access-denied/A 403 is an access decision, not proof that the object is missing. Identify the caller, action and resource; then check matching allows, explicit denies and the applicable public-access or encryption controls.https://sim.shahriarlabs.com/guides/iam-explicit-deny/https://sim.shahriarlabs.com/guides/iam-explicit-deny/A matching explicit deny overrides an allow. First identify which statement applies to the exact action, resource and principal; adding a broader allow cannot cancel that deny.https://sim.shahriarlabs.com/guides/sqs-backlog-keeps-growing/https://sim.shahriarlabs.com/guides/sqs-backlog-keeps-growing/A queue grows when incoming work exceeds completed work over time. Separate arrival rate, worker capacity and retries before increasing concurrency or changing visibility timeout.https://sim.shahriarlabs.com/guides/retry-storm/https://sim.shahriarlabs.com/guides/retry-storm/Retries consume capacity too. Bound attempts, use backoff and jitter, and make side effects idempotent so failure recovery does not amplify load or duplicate work.https://sim.shahriarlabs.com/compare/security-groups-vs-nacls/https://sim.shahriarlabs.com/compare/security-groups-vs-nacls/Security groups apply to associated resources and are stateful. NACLs filter subnet-boundary traffic, support allow and deny rules, and require separate permission for return traffic.https://sim.shahriarlabs.com/compare/nat-gateway-vs-internet-gateway/https://sim.shahriarlabs.com/compare/nat-gateway-vs-internet-gateway/An internet gateway provides a VPC internet path for appropriately addressed resources. Public NAT lets private IPv4 resources initiate internet connections through a translated public address.https://sim.shahriarlabs.com/compare/iam-users-vs-roles/https://sim.shahriarlabs.com/compare/iam-users-vs-roles/IAM users identify account identities that can have long-lived credentials. Roles are assumed to obtain temporary credentials. Prefer suitable federation for people and roles for workloads.https://sim.shahriarlabs.com/compare/sqs-vs-sns-vs-eventbridge/https://sim.shahriarlabs.com/compare/sqs-vs-sns-vs-eventbridge/Use SQS to buffer work for consumers, SNS to publish to subscribers, and EventBridge to route events using rules. They can be combined when a system needs both routing and durable buffering.