> For the complete documentation index, see [llms.txt](https://docs.lingoql.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lingoql.com/introduction/troubleshooting-deploys/runtime-and-startup-failures.md).

# Runtime and startup failures

A runtime failure means the build passed, but the app did not stay up.

On LingoQL, a failed rollout does not replace a healthy deploy.

### App exits immediately

Your start process must keep running.

If the command finishes, the deploy stops.

Common causes:

* running a migration instead of the server
* using a dev command that exits in production
* starting a script that never launches the app

### Port binding issues

Your app must listen on the port provided by `PORT`.

LingoQL also injects `HOST`.

Use `HOST` and `PORT` when your framework supports both values.

If your framework needs a literal host, bind to `0.0.0.0`.

These patterns fail in production:

* hardcoding `3000`
* binding to `127.0.0.1`
* binding to `localhost`

### Missing environment variables

A build can pass even when runtime secrets are missing.

Check every value the app needs to boot:

* database connection strings
* API keys and secret keys
* app base URLs and callback URLs

If the app crashes before serving traffic, missing env vars are one of the first things to check.

### Slow boot or failed health checks

Your app must become healthy after startup.

Long blocking tasks during boot can make the deploy look dead.

Move non-essential work out of the boot path when possible.

Examples include:

* large data syncs
* expensive warmup work
* long migrations

### Database and service connection errors

If the app starts locally but crashes in production, check outbound service dependencies next.

Confirm:

* the connection string is valid
* SSL settings match the provider requirements
* the target service accepts connections from your app

Many managed TCP services on LingoQL require TLS on `443` and SNI set to the service hostname.

Redis-compatible services also require a `rediss://` connection string or explicit TLS enablement in the client.

If the client supports a TLS `servername`, set it to the exact host from your service URL.

Make startup failures log the real exception.

A clear startup error is easier to fix than a silent retry loop.

Use [Services you can deploy](/introduction/services-you-can-deploy.md) for working connection examples for Redis, immudb, Neo4j, ScyllaDB, RabbitMQ, ClickHouse, and Memcached.

### Resource pressure

If the app boots, then crashes under load, it may need more memory or CPU.

Common signs include repeated restarts, timeouts, or out-of-memory errors.

Reduce memory usage in the app first.

If needed, increase the resources assigned to the deploy.

### Quick recovery checklist

1. Confirm the start command launches the server.
2. Confirm the app binds to `HOST:$PORT` or `0.0.0.0:$PORT`.
3. Recheck every required env var.
4. Review the first runtime error in logs.
5. Increase resources if the process is being killed.


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