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Connect pipelines, cloud fundamentals, and deployment troubleshooting.

DNS resolves names to records, load balancers select healthy destinations, IAM controls identities and permissions, and secret managers store sensitive credentials. These components connect an application to users and dependencies without putting all configuration into code. A failure at any layer can look like “the API is down” from the outside.

Each container has its own network context, so localhost points back to that container rather than a sibling service. Reaching a database requires the correct address, network path, credentials and an accepting database process. Compose startup order can start a process without guaranteeing it has finished initialization.

A container stays running while its main process remains alive. An immediate exit usually means the command finished, failed startup or was killed, rather than that Docker randomly stopped a healthy application. Logs, exit status and runtime configuration tell you which case occurred.

A local/CI mismatch means the test depends on something that differs between environments. Common differences include runtime versions, installed files, operating-system behavior, time, service availability or test order. Reproducing the CI command in a clean setup exposes these hidden assumptions.

Rollback restores a previously working application version after a harmful release. It works only if that version is compatible with the current database, message formats and configuration. A complete rollback plan includes health verification and a way to preserve or reconcile work already performed by the new version.

An unreachable cloud API may fail before the request reaches application code. DNS, TLS, routing, firewall rules, load-balancer health and listening ports are separate layers to verify. Checking them in order avoids opening broad access or restarting healthy services without evidence.

DNS resolves names to records, load balancers select healthy destinations, IAM controls identities and permissions, and secret managers store sensitive credentials. These components connect an application to users and dependencies without putting all configuration into code. A failure at any layer can look like “the API is down” from the outside.

Delivery & cloud learning module