Health check
A health check is an assessment or probe that determines whether a system, service, or component is functioning acceptably according to defined criteria.
Learn Docker in a Month of Lunches, Second Edition
A health check is an automated test that determines whether an application is functioning correctly rather than merely having a running process.
- How it is used
- Makes application failures visible when a container’s main process is still running.
- How deep it goes
- Works through Dockerfile checks, container inspection, custom utilities, and Compose timing settings; defers production replacement to a container platform.
- Examples
- Uses an API that returns HTTP 500 after three requests and an exercise checking a Node.js app’s simulated memory use.
- What you can do after
- Operate/configure it in Docker images and Compose, then inspect whether a running application has become unhealthy.
Read how Learn Docker in a Month of Lunches, Second Edition explains health check →
Quarkus in Action
A health check is an evaluation that reports whether an application or one of its dependencies is functioning correctly, typically with a binary outcome.
- How it is used
- Reports application or dependency health for manual monitoring and Kubernetes probes.
- How deep it goes
- Works through an automatic JDBC readiness check and a custom wellness implementation, without detailing Kubernetes probe configuration.
- Examples
- Uses an Inventory service’s MySQL connection failure and an inventory-count wellness check.
- What you can do after
- Apply it via Quarkus SmallRye Health to inspect automatic checks and implement a custom wellness check.
Amazon Web Services in Action, Third Edition: An in-depth guide to AWS
A health check is an automated test that determines whether a website or backend target is able to receive traffic and provide an expected response.
- How it is used
- Keeps load-balancer traffic on healthy targets and detects website outages through an external scheduled check.
- How deep it goes
- Walks through console-based scheduling and gives concrete target-group settings, but does not detail health-check algorithms.
- Examples
- Uses a website GET request with expected text and a target-group check of `/index.html` accepting HTTP 200–299.
- What you can do after
- Operate/configure it with a Lambda blueprint and scheduled rule, or with Application Load Balancer target-group settings.
Build and Orchestrator in Go (From Scratch)
A health check is an operation that evaluates whether a running task is functioning normally, typically by calling an endpoint and interpreting its response.
- How it is used
- Drives automatic task recovery by polling task endpoints and restarting unhealthy or failed tasks.
- How deep it goes
- Works through task fields, URL construction, Docker port lookup, polling, state updates, and bounded restart logic.
- Examples
- Demonstrates an echo service whose /health returns 200 and /healthfail returns 500, then observes restarts.
- What you can do after
- Operate/configure it by declaring a task endpoint and using health-check results to trigger bounded restarts.
Read how Build and Orchestrator in Go (From Scratch) explains health check →
Machine Learning Platform Engineering
A diagnostic test that determines whether a service or execution unit is functioning and able to handle requests.
- How it is used
- Supports Kubernetes monitoring, pod management, traffic gating, and troubleshooting for deployed model services.
- How deep it goes
- Defines health, liveness, and readiness roles with endpoint behavior, but does not detail custom implementation code.
- Examples
- Uses /healthz and /readyz endpoints, pod initialization failures, BentoML services, and Kubernetes probe behavior.
- What you can do after
- Operate/configure deployed services with liveness and readiness monitoring in Kubernetes environments.
Read how Machine Learning Platform Engineering explains health check →
Build Financial Software with Generative AI (From Scratch)
A health check is an automated test or status evaluation that determines whether an application or runtime component is functioning acceptably.
- How it is used
- Monitors container and application status in a multi-container system, supporting alerts, restarts, and production self-healing.
- How deep it goes
- Distinguishes application endpoints from Docker checks and configures PostgreSQL readiness with intervals, timeouts, startup delay, and retries.
- Examples
- Uses a health_check database table, a PostgreSQL pg_isready command, formatted docker ps output, and API documentation at localhost:8000/docs.
- What you can do after
- Operate/configure it by adding a PostgreSQL Docker health check and inspecting its healthy status with docker ps.
Read how Build Financial Software with Generative AI (From Scratch) explains health check →
Bootstrapping Microservices, Second Edition: With Docker, Kubernetes, GitHub Actions, and Terraform
A health check is an automated assessment of whether a running service or workload is functioning and available according to defined criteria.
- How it is used
- Uses automated checks to monitor microservice availability and trigger protective action in production.
- How deep it goes
- Defines readiness and liveness probes and shows their Kubernetes configuration, but does not detail probe implementation logic.
- Examples
- Uses gateway HTTP endpoints, Kubernetes Deployment YAML, RabbitMQ startup, and Kubernetes pod restarts as concrete examples.
- What you can do after
- Operate/configure Kubernetes probes that delay traffic until readiness and restart workloads that fail liveness checks.
Kubernetes for Developers
A health check is an operational test or signal indicating whether an application or process is functioning correctly.
- How it is used
- Uses application health signals to keep deployments available and route traffic only to ready replicas.
- How deep it goes
- Explains liveness, readiness, failure conditions, and HTTP, TCP, and Bash implementations, stopping short of exhaustive configuration guidance.
- Examples
- Demonstrates /healthz over HTTP, TCP connectivity on port 25, and Bash tests for background tasks.
- What you can do after
- Operate/configure Kubernetes probes that restart unhealthy containers and protect traffic during application updates.
Building Distributed Applications that Work
A health check is an automated assessment of whether an application or dependency is ready and functioning sufficiently for interaction.
- How it is used
- Uses endpoint responses to let Aspire assess whether services are ready to interact with other systems.
- How deep it goes
- Implements a self-check and maps basic and live-tag endpoints, while leaving production protections scenario-specific.
- Examples
- Uses a self-check tagged live and /health and /alive endpoints, with /alive filtering checks by tag.
- What you can do after
- Configure health-check registrations and HTTP endpoints for Aspire-hosted applications.
Read how Building Distributed Applications that Work explains health check →
Related concepts
- liveness checkincludes · A liveness check is an automated health test that determines whether a running workload remains functional or should be restarted.
- readiness checkincludes · A readiness check is a health probe that determines whether a running service or workload is prepared to receive requests or traffic.
- auto-scaling groupused by · An auto-scaling group is a managed collection of compute instances whose capacity is automatically adjusted according to configured policies, conditions, or workload demand.
- uptimemeasures · Uptime is the duration or proportion of a specified period during which a system or service is operational and available to provide its intended function.
- Docker Swarm manager nodeused by · A Docker Swarm manager node coordinates the cluster, schedules services and tasks, maintains swarm state, and directs worker nodes.
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