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What “connection refused” means in a Rails deployment
PostgreSQL uses the phrase for a client that cannot find a server to talk to at the requested TCP endpoint or Unix socket. The message does not mean that PostgreSQL received your request and rejected your credentials. As the PostgreSQL Global Development Group puts it, “Connection refused in this context does not mean that the server got your connection request and rejected it.”
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That distinction determines your first move. Authentication errors happen after a server is reached; a refused connection happens before authentication. Rotating a password, changing a Rails model, or rerunning a migration cannot make a process start listening on the required endpoint.
| Exception detail | What it tells you | First check |
|---|---|---|
connection refused with a host and port |
No PostgreSQL listener answered at that TCP address, or the route is being refused. | Run pg_isready against the same host and port. |
No such file or directory for a Unix socket |
The expected local socket directory or socket file is absent. | Check whether PostgreSQL is running locally and whether Rails is unintentionally using a socket. |
Password, authentication, or pg_hba.conf rejection |
A server was reached and proceeded to access control. | Inspect credentials, SSL settings, and host-based authentication after connectivity is confirmed. |
PostgreSQL’s default TCP port is 5432 (PostgreSQL 16 documentation). Its default listen_addresses value is localhost, which allows loopback clients but not a separately hosted application. A production app therefore needs an address, port, firewall path, and authentication policy that are deliberately configured for its deployment topology.
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Use the endpoint in the exception as your evidence
Do not begin with assumptions about where the database ought to be. Read the complete exception and record:
- the hostname or IP address;
- the port number;
- the database name, if Rails prints it;
- the Unix socket directory or file path, if the error is socket-based; and
- whether the failing release, web process, worker, or one-off command produced the message.
A surprising value is often the diagnosis. A production process trying localhost:5432 is not reaching a managed database elsewhere. A container using a private hostname from another network, or a URL with an old port, has the same practical problem even when PostgreSQL itself is healthy.
A repeatable diagnostic sequence
1. Preserve and redact the failing connection details
Copy the endpoint into your incident notes before changing variables. If the exception contains a full URL, remove the password before sharing logs. Keep the host, port, database, and socket path intact; those are the values needed for diagnosis.
Check the process environment without printing a secret-bearing URL to a public log. This Ruby command reports the URL’s scheme, host, port, and path while leaving user information and the password out of the output:
ruby -ruri -e 'u = URI(ENV.fetch("DATABASE_URL")); puts({scheme: u.scheme, host: u.host, port: u.port, database: u.path}.inspect)'If the variable is absent, the command raises a missing-key error. That absence is itself useful: Rails may then fall back to values in config/database.yml, a local socket, or a localhost TCP endpoint.
2. Probe exactly the same host and port
From the same runtime environment as the Rails release or application process, run:
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pg_isready -h "$DB_HOST" -p "$DB_PORT"Substitute the host and port recorded from the exception. For a socket error, use the socket directory shown in the message, for example:
pg_isready -h /path/to/socket-directory -p 5432pg_isready is a readiness probe, not a password test. PostgreSQL documents these exit statuses:
| Exit status | Meaning | Next action |
|---|---|---|
| 0 | The server is accepting connections. | Move up the stack: compare Rails’ URL, SSL options, credentials, and database name with the working endpoint. |
| 1 | The server is rejecting connections, commonly while starting. | Wait for startup to finish, inspect database logs, and probe again before releasing migrations. |
| 2 | No response was received. | Check the hostname, route, firewall or security group, port, listener interface, and whether the service is running. |
A successful readiness check proves that something at that endpoint is accepting PostgreSQL connections; it does not prove that Rails has the right password, database, SSL mode, or permissions. Conversely, a failed probe against a different host is not evidence about the endpoint Rails actually used.
3. Confirm production’s DATABASE_URL
Rails combines DATABASE_URL with config/database.yml. When the URL is present, its adapter and database values cannot be replaced by corresponding values in database.yml. This precedence can make an apparently correct YAML file irrelevant if the deployment platform injects an outdated or malformed URL.
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DATABASE_URLexists in the release, web, and worker contexts that need it;- the URL uses the expected PostgreSQL scheme and points to the provider’s current hostname;
- the port is the provider’s port rather than an assumed local
5432; - the path names the intended database;
- the username is the one provisioned for that database; and
- SSL parameters required by the provider are present.
Check the variable in the platform’s dashboard or secret store as well as inside a one-off shell. A value configured for a web service may not automatically exist in a separate release command, worker, preview environment, or review app.
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4. Verify the PostgreSQL adapter and URL scheme
A PostgreSQL-backed Rails application must include the pg gem in its Gemfile and deploy it in the production bundle. A missing or development-only adapter normally produces a different error, but checking it prevents you from chasing a network symptom with an incomplete runtime.
Confirm that the connection URL identifies PostgreSQL and that the deployed bundle contains the same adapter expected by the Rails environment. If a platform supplies a URL with SSL requirements, preserve those parameters instead of replacing the entire URL with a hand-written localhost value.
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A migration command cannot repair a refused socket. First make the readiness probe succeed from the deployment environment. Then run the platform’s release, build, or pre-deploy migration hook. If a migration fails after pg_isready reports status 0, investigate authentication, database existence, permissions, schema state, or SSL negotiation rather than listener availability.
Why Rails tries localhost in production
The production variable was never injected
The most common explanation is a missing DATABASE_URL. Rails then uses the production section of config/database.yml. If that section omits a remote host, the PostgreSQL client can default to a local Unix socket or local TCP loopback. In a container or hosted dyno, “local” means that isolated machine, not your development computer and not a provider-managed database.
The wrong environment received the variable
Deployment systems often separate build, release, web, worker, and one-off command environments. A URL present during image creation may be absent during the release command, while a preview environment may retain a different value from production. Inspect the environment at the exact phase that logged the error.
A stale URL overrides correct YAML
Because Rails merges the URL with database.yml and gives the URL authority over adapter and database values, a stale platform secret can keep directing Rails to localhost even after YAML is fixed. Replace or remove the stale variable, redeploy the process that reads it, and re-run the endpoint probe.
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The URL was parsed differently than intended
Special characters in passwords must be URL-encoded. An unescaped character can truncate the password or alter parsing. That usually leads to authentication or parsing errors, but it can also leave the client with an unintended host or port. Inspect the parsed scheme, host, port, and path without exposing credentials.
Fixing a self-hosted PostgreSQL endpoint
Confirm the database service is running
On a self-managed server, verify that the PostgreSQL service is started and review its startup log. A service still initializing can produce readiness status 1; a stopped service generally produces status 2 or a refused TCP connection. Probe repeatedly during a controlled restart rather than launching migrations while startup is incomplete.
Check the listener and port
PostgreSQL listens on port 5432 by default, but administrators can change it. Compare the configured port with the port in Rails’ URL and with the port exposed by the host or container. Confirm that a PostgreSQL process is listening on the expected interface, not only on an internal address that the application cannot route to.
The default listen_addresses=localhost permits local loopback TCP connections only. A remote Rails process requires a reachable interface, a firewall or security-group rule allowing the chosen port, and a host name that resolves to the correct network. Exposing PostgreSQL broadly is not a safe shortcut: restrict inbound sources to the application network and use encrypted connections where the provider or topology requires them.
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Match pg_hba.conf to the application network
After the listener and route work, PostgreSQL’s host-based authentication file, pg_hba.conf, must contain a rule that matches the application’s source address, database, user, and authentication method. A mismatch here normally changes the symptom from “connection refused” to an explicit access rejection, which is progress because the server has been reached.
Restart after startup-only settings change
Settings read when the server starts, including listener configuration, require a PostgreSQL restart after editing. Restart during a maintenance window, wait for readiness status 0, and only then release application traffic or migrations. Keep the firewall rule, listener address, port, and pg_hba.conf policy consistent; changing one layer cannot compensate for a blocked layer elsewhere.
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Provider-specific wiring
Render
- Open the web service’s environment settings and set
DATABASE_URLto the Render Postgres connection string for the intended database. - Ensure the value is available to the release or pre-deploy phase that runs Rails commands, not only to the running web process.
- Provide
RAILS_MASTER_KEYwhen the application requires encrypted Rails credentials during build or boot. - Configure migrations in the build or pre-deploy command according to the service’s deployment flow.
- Deploy, open a shell in the same service context, and run
pg_isreadyagainst the host and port parsed from the URL before treating a migration failure as a schema problem.
The important Render distinction is wiring: the web service must receive the managed database endpoint, and the migration hook must run only after that endpoint is reachable.
Heroku
- Attach or provision Heroku Postgres for the application and use the connection configuration Heroku supplies rather than a localhost fallback.
- Keep the
pggem in the production bundle. - Account for Heroku Postgres TLS. Heroku’s current connection documentation (2026) requires TLS 1.2 or higher.
- If the client or driver requires it, include
sslmode=requirein the connection configuration while preserving the supplied host, port, database, and credentials. - Run the release migration only after a one-off command can reach the attached database.
A successful local connection does not validate a Heroku deployment if local PostgreSQL permits unencrypted loopback traffic while the hosted database requires TLS.
Fly.io
- Attach Managed Postgres to the Fly.io application using the platform’s supported integration.
- Confirm that the attachment stores the resulting
DATABASE_URLas an application secret and that the deployed process can read it. - Inspect the parsed host, port, and database from a Fly.io machine or release context; do not assume the endpoint is localhost.
- Place Rails migrations in the app’s
release_commandso they run as a release step rather than once per web machine. - Probe readiness before allowing the release command to proceed, and inspect service logs if the database is still starting.
Fly.io’s key failure mode is an incomplete attachment or a secret available to one process but not to the release process. Correct the attachment and secret first; changing Rails schema code will not fix a missing route.
Compare fixes by the layer they repair
| Fix path | Database model | How DATABASE_URL arrives |
Listener and firewall work | SSL/TLS consideration | Migration timing |
|---|---|---|---|---|---|
| Render Postgres | Managed PostgreSQL | Set the web service variable to the Render Postgres connection string. | Provider manages the database listener; the service must use the reachable provider endpoint. | Use the parameters supplied by the connection string. | Build or pre-deploy command. |
| Heroku Postgres | Managed PostgreSQL attached to the app | Use the attached Heroku configuration. | Provider manages listener access. | TLS 1.2 or higher; some clients require sslmode=require. |
Run in the application’s release flow after connectivity. |
| Fly.io Managed Postgres | Managed PostgreSQL attached to the app | Attachment stores DATABASE_URL as an app secret. |
Use the attachment’s network endpoint, not localhost. | Follow the supplied connection parameters. | release_command. |
| Self-hosted PostgreSQL | Your own server or private network | You provision and inject the URL. | You must configure listener address, port, routing, firewall or security group, and pg_hba.conf. |
Configure encryption and client parameters appropriate to the network. | Your release or pre-deploy hook, after readiness. |
This comparison prevents a missing provider attachment from being misdiagnosed as a bad password. Managed services remove much of the listener administration, but they still require the application to receive the correct URL and to honor provider TLS settings.
Branch troubleshooting by the probe result
pg_isready returns status 2
- Recheck the hostname for a typo, stale database, or wrong environment.
- Verify DNS resolution and that the application network can route to the address.
- Confirm the port in the URL matches the provider or self-hosted listener.
- Inspect firewall, security-group, private-network, and container-exposure rules.
- On self-hosted PostgreSQL, verify the service is running and not listening only on localhost.
pg_isready returns status 1
- Inspect PostgreSQL startup and recovery logs.
- Wait for initialization or failover to complete and probe again.
- Do not run migrations repeatedly while the server is rejecting startup connections.
pg_isready returns status 0 but Rails still fails
- Compare the exact host and port Rails parses with the values you probed; Rails may be using another environment or URL.
- Check database name, username, password encoding, and SSL parameters.
- Confirm the
pggem is included in the production bundle. - Look for an authentication, authorization, certificate, or database-not-found error that replaced the original refusal.
The exception names a Unix socket
- Determine whether the deployment is supposed to use a local PostgreSQL service. If not, inject a TCP
DATABASE_URLso Rails does not fall back to a socket. - If local PostgreSQL is intended, verify the socket directory and file exist and that the service created them.
- Check permissions for the process user and confirm the socket path in Rails matches the server’s configured path.
The endpoint is correct but connections fail intermittently
Separate startup timing from permanent configuration. A provider database waking, recovering, or failing over may briefly return readiness status 1. A permanently refused connection points back to listener, route, firewall, or port configuration. Capture timestamps, probe from the release environment, and correlate them with database and platform logs before changing credentials.
Release checklist before trying the deploy again
- The exception’s host, port, and socket path were recorded.
pg_isreadysucceeds from the same environment that runs Rails.DATABASE_URLexists in every required process and release context.- The URL’s scheme, host, port, database, and SSL options match the provider.
- The production bundle includes the
pggem. - Self-hosted PostgreSQL listens on a reachable interface and port.
- Firewall or security-group rules allow only the required application network.
pg_hba.confpermits the application source, user, and database.- Provider-specific secrets such as
RAILS_MASTER_KEYare present when required. - Migrations are attached to the correct build, pre-deploy, or release hook.
- The migration hook runs only after database readiness is established.
What not to do
- Do not rotate passwords first. A refused connection has not reached authentication.
- Do not hard-code localhost in production. It points to the application host or container, not automatically to a managed database.
- Do not expose PostgreSQL to the entire internet as a quick fix. Correct the route and restrict network sources.
- Do not treat a migration retry as a connectivity test. Use
pg_isreadyagainst the exact endpoint first. - Do not assume
database.ymlwins. A presentDATABASE_URLsupplies authoritative adapter and database values.
Final diagnosis
When Rails reports PG::ConnectionBad: connection refused, start at the endpoint, not at the password. Test the printed host, port, or socket; establish whether PostgreSQL is listening; then make production’s DATABASE_URL, provider attachment, listener address, firewall, SSL settings, and migration hook agree. Once pg_isready reports an accepting server from the deployment environment, any remaining failure is a higher-layer configuration issue that can be diagnosed with the now-reachable database.
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