Ansible Playbook & Connection Errors

Understanding Ansible errors

Ansible errors split cleanly between transport problems (it cannot reach or authenticate to the host) and execution problems (it reached the host but the play failed). The message header tells you which: UNREACHABLE! is transport, FAILED! is execution. Transport issues are SSH issues wearing an Ansible hat and should be debugged with plain ssh first.

How to debug Ansible errors

1. Run ansible -m ping all before running any playbook. It isolates connectivity and privilege escalation from your task logic.
2. Raise verbosity progressively: -v shows results, -vvv shows the SSH command line, -vvvv shows connection debugging. Most unreachable errors are solved at -vvv.
3. Use --check --diff to see what a play would change without changing it. This turns a destructive debugging loop into a safe one.
4. For undefined-variable errors, dump the actual scope with a debug task (var: hostvars[inventory_hostname]) rather than reasoning about precedence from the docs.
5. Remember variable precedence order: extra vars (-e) beat everything, role defaults lose to everything. Surprising values are nearly always a precedence surprise.

Tools worth reaching for

• ansible -m ping
• ansible-playbook --check --diff
• ansible-lint
• ssh -vvv

All 10 Ansible errors

• Ansible: 'variable' is undefinedA variable used in a playbook or template was not defined in inventory, group_vars, host_vars, or the playbook itself.
• Ansible: Host unreachableCannot connect to target host via SSH. Network issues, wrong IP, SSH not running, or key authentication failed.
• Ansible: Jinja2 template errorA Jinja2 template in a playbook or template file has a syntax error such as unclosed braces, undefined filters, or bad…
• Ansible: Module not foundSpecified module doesn't exist or isn't installed. Wrong module name or collection not installed.
• Ansible: Playbook syntax errorYAML syntax error in playbook. Indentation issues, invalid YAML, or missing required fields.
• Ansible: Privilege escalation password requiredTask requires sudo but password not provided. Target user needs sudo password for privilege escalation.
• Ansible: SSH connection timeoutAnsible timed out trying to establish an SSH connection to the target host. The host may be unreachable, the SSH…
• Ansible: The conditional check 'result.rc == 0' failed NewThe when expression could not be evaluated, usually because the variable it names does not exist on this host: the…
• Ansible: Vault password not providedA playbook uses encrypted vault variables but no vault password was supplied at runtime.
• Ansible: you must install the sshpass program NewOpenSSH refuses to read a password from anything but a terminal, so Ansible shells out to sshpass whenever a…

Other categories

• AI 35Rate limits, context windows, GPU memory and model-serving failures.
• API 14Auth headers, payload limits, versioning, idempotency and webhook signatures.
• Apple 10Command line tools, dyld, Homebrew permissions, notarisation and Keychain.
• Auth 11OIDC, SAML, Auth0, Okta, Keycloak, passkeys and MFA failures.
• BigData 11Spark, Kafka, Airflow, Snowflake, Flink and Databricks failures.
• C# 12NuGet restore, null references, EF Core migrations, async deadlocks and Blazor…
• C++ 11Segfaults, linker errors, memory corruption and template deduction failures.
• Caching 10Cache stampedes, stale content, Varnish and CloudFront failures.
• CI/CD 18GitHub Actions, GitLab CI, Jenkins, CircleCI: permissions, runners and…
• Client 21CORS, mixed content, module resolution, memory limits and framework runtime…
• Cloud 25IAM permissions, quotas, service limits and credential failures.
• Dart 10Null safety, pub version solving and build toolchain problems.
• Database 41Connections, deadlocks, constraints, replication and memory limits.
• DNS 10NXDOMAIN, SERVFAIL, timeouts, propagation and delegation problems.
• Docker 27Daemon connectivity, disk space, image pulls, ports and architecture mismatches.
• Elixir 9GenServer timeouts, supervision failures and Mix compilation problems.
• Email 8Delivery failures, relay denial, authentication, SPF, DKIM and DMARC.
• Frontend 23Hydration mismatches, bundler resolution, layout shift and font loading.
• Git 20Merge conflicts, rejected pushes, detached HEAD, LFS and repository corruption.
• Go 19Nil map assignment, concurrent map access, context cancellation and deadlocks.
• GraphQL 13Validation, depth limits, N+1 queries and fragment problems.
• gRPC 10Status codes, deadlines, message limits, TLS and HTTP/2 transport failures.
• HTTP 494xx client errors, 5xx server errors, redirects, headers and protocol problems.
• ICMP 23Destination unreachable, time exceeded, fragmentation needed and redirects.
• Ingress 8404 default backend, missing TLS secrets, IngressClass and path matching.
• Java 19Class loading, dependency resolution, connection pools and JVM version…
• JavaScript 42npm resolution, async pitfalls, hydration, memory limits and runtime type…
• Kubernetes 34CrashLoopBackOff, ImagePullBackOff, OOMKilled, RBAC, scheduling and storage.
• Logging 9Log4j, Logback, Fluentd, Logstash and CloudWatch ingestion problems.
• MessageQueue 14Kafka, RabbitMQ, SQS, NATS and Celery: lag, rebalancing and poison messages.
• Mobile 17Gradle, CocoaPods, Xcode signing, Metro bundler and toolchain mismatches.
• Monitoring 12Prometheus scrapes, Grafana data sources, OpenTelemetry exporters and agent…
• Network 35Refused connections, timeouts, resets, MTU problems and port exhaustion.
• Performance 6GC pauses, thread pool starvation and event loop blocking.
• PHP 11Memory limits, execution timeouts, autoloading, Composer and PDO connections.
• Proxy 17nginx, Envoy, HAProxy, Traefik, Caddy and Cloudflare upstream failures.
• Python 35Imports, virtual environments, encoding, concurrency and dependency conflicts.
• Regex 8Catastrophic backtracking, back references, escaping and engine differences.
• Ruby 11Bundler, migrations, native extensions, encoding and asset compilation.
• Rust 19Borrow checker, ownership moves, trait bounds and lifetime mismatches.
• Scala 6Dependency resolution, binary compatibility and type inference failures.
• Security 25JWT validation, CSRF, OAuth grants, SELinux, SSH host keys and CSP.
• Serverless 11Lambda timeouts, package size limits, VPC networking and cold starts.
• Shell 13Command not found, permissions, quoting, expansion and Makefile syntax.
• Storage 13S3 permissions, NFS mounts, quotas, signed URLs and volume attachment.
• Svelte 10Store subscriptions, load functions and server/client boundaries.
• System 26Disk space, systemd units, file descriptors, OOM killer and scheduled jobs.
• Terraform 18State locks, provider auth, drift, dependency cycles and plan-time unknowns.
• Testing 18Jest, pytest, JUnit, Cypress and Playwright: fixtures, snapshots and timeouts.
• TLS 24Untrusted authorities, expiry, hostname mismatch, chains and cipher negotiation.
• TypeScript 19Assignability, missing declarations, strict null checks and generic constraints.
• Virtualization 8VirtualBox, VMware, Hyper-V, WSL, KVM and hypervisor conflicts.
• Web3 7Gas estimation, nonce management and reverted transactions.
• WebAssembly 7Compile errors, memory bounds and host binding mismatches.
• WebServer 10nginx, Apache, IIS and Caddy: binding, permissions, rewrites and TLS.
• Windows 10Installer failures, missing runtimes, update errors and permission problems.