Your MCP server cannot reach Postgres. Debug the boundary in this order

#postgres #mcp #database #ai

When an MCP server cannot reach Postgres, the model is usually the least interesting part of the failure.

The break is normally lower in the stack:

configuration precedence
DNS and routing
TLS negotiation
pg_hba.conf
authentication
authorization
pooling and timeouts

Debug those layers in that order.

Start by recording the host, port, database, username, and SSL mode the runtime actually resolved. Do not log the password.

Then prove reachability from the MCP runtime, not from your laptop. A container or private endpoint may have a completely different route.

If PostgreSQL returns a host-rule error, capture the source address, user, database, and SSL state. Add the narrowest matching rule, reload, and verify the active identity after reconnecting.

A successful password is not the finish line either. Test that the role can read the approved view and cannot mutate data or inspect excluded schemas.

Finally, run a known read-only query and retain a receipt: database identity, source, row count, truncation state, and elapsed time.

The goal is not "connected."

It is "connected as the expected identity, through the expected route, with the expected scope."

The full diagnostic sequence is here: MCP server Postgres connection troubleshooting