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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsBuild uptime monitoring as four distinct checks: whether the API process is alive, whether it is ready for traffic, whether PostgreSQL accepts connections, and whether the application can complete a small database operation through its real request path. Each signal answers a different question; none should be mistaken for a complete diagnosis.
Why use four signals instead of one health check?
A single green status can conceal important failures. PostgreSQL may accept connections while an application role lacks access to a required table, or an API process may respond even though it should not receive traffic. Keep checks separate and name each response according to what it measures.
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The distinction is operational: use liveness to detect a process that is no longer responding, readiness to decide whether an instance should receive traffic, PostgreSQL connection status to assess the server’s ability to accept clients, and an application-level operation to check a narrow part of the database path the application depends on.
1. Is the API process alive?
A liveness check should answer only whether the service process is responding. Avoid making it depend on every external service: if a database outage makes liveness fail, an orchestrator may restart otherwise functioning API processes repeatedly without resolving the underlying problem.
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Health endpoint conventions vary by product. Prometheus documents /-/healthy as a health endpoint, while PostgREST’s /live checks whether PostgREST is running on its configured port. These are product-specific examples, not universal endpoint names. See the Prometheus Management API documentation and PostgREST 12.2 Admin Server documentation.
2. Should this API instance receive traffic?
Readiness answers whether an instance can serve requests now. It can include required dependencies as well as the API’s own state, so a process can be live while not ready.
PostgREST 12.2 provides a concrete example: its /ready endpoint checks the connection pool and schema cache in addition to liveness. It returns HTTP 200 when those checks are good and HTTP 503 when they are not. Treat those paths and semantics as PostgREST-specific; define and document the equivalent contract for your own API.
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Make the readiness response useful to the traffic router, not a detailed diagnostic report. A stable success or failure status lets routing systems make a decision without exposing credentials, schema details, or internal error messages.
3. Is PostgreSQL accepting connections?
PostgreSQL’s pg_isready checks server connection status. Its exit status distinguishes four outcomes:
| Exit status | Meaning |
|---|---|
| 0 | The server is accepting connections. |
| 1 | The server is rejecting connections. |
| 2 | No response was received. |
| 3 | No connection attempt was made, for example because parameters were invalid. |
These meanings are documented for PostgreSQL 16 in the pg_isready reference. The command can report server status without correct credentials, but incorrect supplied values may cause the server to log a failed connection attempt. A successful result means PostgreSQL is accepting connections; it does not prove that your application’s credentials, role, schema, query, or full request path works.
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4. Can the application complete a bounded database operation?
For an application-level signal, exercise a small operation through the same relevant connection configuration, permissions, and schema path used by real requests. This fills the gap between “the server accepts connections” and “the application can do the database work it depends on.”
The exact operation depends on the service. Choose the smallest read or other safe operation that verifies a critical dependency, keep its work bounded, and give it a timeout appropriate to the endpoint’s purpose. Avoid writes with lasting side effects. Return only a generic status; log or collect diagnostic details through access-controlled operational channels instead.
This is an engineering pattern, not a prescribed PostgreSQL or PostgREST endpoint contract. Keep its result distinct from a basic connection check, and avoid treating it as proof that every possible request will succeed.
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How to put the checks into an operational design
Choose a contract for each signal
- Liveness: process response only; used to identify an unresponsive service.
- Readiness: whether the instance should currently receive traffic, including dependencies required to serve requests.
- PostgreSQL acceptance: whether the server is accepting connections, using
pg_isreadyor an equivalent check. - Application operation: whether a small, bounded database task works through the application’s relevant permissions and schema.
Keep routing and alerting decisions separate
Not every failure should have the same consequence. Readiness is intended to inform traffic routing. Liveness is about the process itself. PostgreSQL status and application-operation checks can help alerting and investigation, but decide deliberately whether either one should remove an instance from service. A dependency outage may affect every instance at once, and restarting all of them will not repair the database.
Set limits and avoid leaking details
- Set a timeout so a stalled dependency cannot make the health request stall indefinitely.
- Keep the database operation small and predictable; account for its frequency and resource cost.
- Return stable status codes and a clear, documented meaning for each endpoint.
- Keep credentials, SQL errors, host details, and schema information out of public responses.
- Test failure states deliberately so operators know which signal changes when the process, dependency, or application operation is unavailable.
What to inspect when a check fails
A health response is a compact status signal, not a diagnosis. PostgreSQL’s monitoring chapter frames the operator’s question as “What is the system doing right now?” It describes database statistics views including pg_stat_activity, pg_stat_replication, and pg_stat_database, and also identifies operating-system tools such as ps, top, iostat, and vmstat. Use the check that failed to guide investigation rather than assuming every failure is a database outage. See PostgreSQL 17: Monitoring Database Activity.
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How to compare health-check implementations
When evaluating implementations, compare what each one actually covers rather than relying on a generic “healthy” label:
- Coverage: process, dependencies, or an application operation.
- Failure distinctions: whether it separates rejection, no response, invalid configuration, or application-level failure.
- Cost and timeout: how much work it adds and how long it can wait.
- Intended consumer: whether the response is for traffic routing, alerting, or operator investigation.
The PostgreSQL wiki maintains a category-level list of monitoring checkers and metrics exporters, including prometheus/postgres_exporter, pgexporter, and pgSCV. The list is a starting point for finding monitoring approaches, not a claim that any one tool provides all four signals: PostgreSQL Wiki: Monitoring.
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