Unable to start DynamoDB Local process

TL;DR — DynamoDB Local (a Java app) couldn't launch. The usual causes are a missing or too-old Java runtime, port 8000 already taken, or the serverless-dynamodb plugin never downloaded the jar. Fix Java, free the port, or re-install.

What it means

You'll see it from the serverless-dynamodb / serverless-dynamodb-local plugin, or when running the jar directly:

Unable to start DynamoDB Local process!

The child process that runs the local emulator failed to spawn or exited immediately.

Why it happens

No Java, or an incompatible version. DynamoDB Local needs a Java runtime — current versions (v2.6.0 and newer, including v3.x) require JRE 17+. If java -version fails, that's it; if it prints an old version, you'll often see UnsupportedClassVersionError in the underlying output.
Port already in use — something else is on 8000 (a previous instance that didn't shut down).
The jar was never installed — sls dynamodb install didn't run or failed, so there's nothing to start.
A path/permissions problem with the install directory.
Apple Silicon / arch mismatch with an old jar that bundles native SQLite libs.

Download failures

When npx serverless dynamodb install or the Maven plugin download fails (network proxy, corporate TLS inspection, or a full disk), the start command finds no jar and exits with the same generic Unable to start DynamoDB Local process! wrapper — check the plugin log for ENOENT or HTTP errors before chasing Java.

How to fix it

Install/verify Java 17+: java -version. If missing or too old, install a current JDK/JRE (e.g. Temurin or Corretto 17+).
Re-install DynamoDB Local:
```
npx serverless dynamodb install
```
Free the port (or change it): find what's on 8000 and stop it —
```
lsof -i :8000   # then kill the PID, or configure a different port
```
Use the official Docker image to sidestep Java/arch issues entirely:
```
docker run -p 8000:8000 amazon/dynamodb-local
```
Docker bundles a compatible JRE — no local Java install required.
Point your client at it with a placeholder region + endpoint (see Missing region in config).

Connect from DynoTable

If Java/arch or a failed jar download blocks Local, run the official Docker image and connect DynoTable without a local JRE (Install DynoTable). In Settings → Profiles → Add Profile, set endpoint http://localhost:8000, pick a placeholder region, and use alphanumeric dummy credentials — then Test Connection. That path avoids the Unable to start DynamoDB Local process! spawn failure entirely. Walkthrough: Running DynamoDB Local. If the plugin never downloaded the jar, re-run npx serverless dynamodb install and confirm the install directory is writable — permission errors surface as the same generic spawn message with no Java stack trace. After Local is up, load fixtures with the DynamoDB JSON converter.

Could not connect to DynamoDB Local
DynamoDB Local UnsupportedClassVersionError — the too-old-Java flavor of this failure.
DynamoDB Local sqlite4java errors — the native-library/arch flavor.
Missing region in config
Learn: Running DynamoDB Local

References

Deploying DynamoDB locally on your computer — AWS DynamoDB Developer Guide (JRE 17+ requirement for v2.6.0+, launch command, default port 8000)
DynamoDB local usage notes — AWS DynamoDB Developer Guide (-port and the other runtime options)
amazon/dynamodb-local — Docker Hub (official image; docker run -p 8000:8000 amazon/dynamodb-local)

Last verified 2026-07-13 against the official AWS documentation linked above.