What causes "Failed to initialize Glue catalog" in apache/druid?

Look at the wrapped cause ('Caused by:' below this RE) for the true error — missing property, credentials, region, or classpath problem — and fix that first.

apache/druid · critical · RE (org.apache.druid.java.util.common.RE)

Failed to initialize Glue catalog

Error message

Failed to initialize Glue catalog

What it means

GlueIcebergCatalog.setupGlueCatalog instantiates the Iceberg GlueCatalog and calls catalog.initialize(CATALOG_NAME, catalogProperties) inside a try block; any exception there is wrapped in RuntimeException("Failed to initialize Glue catalog"). This fires when the AWS Glue-backed Iceberg catalog cannot start — typically due to missing/invalid AWS configuration (region, credentials, warehouse/catalog properties), missing AWS SDK classes on the classpath, or connectivity/permission failures during initialization.

Source

Thrown at extensions-contrib/druid-iceberg-extensions/src/main/java/org/apache/druid/iceberg/input/GlueIcebergCatalog.java:109

    log.info("Glue catalog set [%s].", catalog.toString());
    return catalog;
  }

  private Catalog setupGlueCatalog()
  {
    // We are not passing any hadoop config, third parameter is null
    catalogProperties.put("type", TYPE_KEY);

    // AWS Glue catalog internally uses reflection to locate certain classes from the iceberg-aws dependency.
    // These classes are not available in the current context class loader, and so we explicitly set the context class loader to the system classloader.
    ClassLoader currCtxClassloader = Thread.currentThread().getContextClassLoader();
    try {
      Thread.currentThread().setContextClassLoader(getClass().getClassLoader());
      catalog = new GlueCatalog();
      catalog.initialize(CATALOG_NAME, catalogProperties);
    }
    catch (Exception e) {
      throw new RE(e, "Failed to initialize Glue catalog");
    }
    finally {
      Thread.currentThread().setContextClassLoader(currCtxClassloader);
    }
    return catalog;
  }

  @Override
  public boolean isCaseSensitive()
  {
    return caseSensitive;
  }
}

View on GitHub (pinned to 9b90983fd2)

Solutions

Look at the wrapped cause ('Caused by:' below this RE) for the true error — missing property, credentials, region, or classpath problem — and fix that first.
Verify catalog properties include warehouse, io-impl (e.g. org.apache.iceberg.aws.s3.S3FileIO), and the correct AWS region for your Glue Data Catalog.
Ensure AWS credentials are available (env vars, ~/.aws/credentials, or instance/task IAM role) and the role has glue:GetDatabase/glue:GetTable permissions.
Confirm the druid-iceberg-extensions load spec includes all AWS SDK dependencies and that extension loading is enabled for it in your Druid config.
Test network reachability to the Glue endpoint (glue.<region>.amazonaws.com) from the Druid process; check proxies/VPC endpoints/security groups.

Example fix

// before (inputSourceConfig)
{"type":"iceberg","catalogProperties":{"type":"glue"}}
// after
{"type":"iceberg","catalogProperties":{"type":"glue","warehouse":"s3://my-bucket/warehouse/","io-impl":"org.apache.iceberg.aws.s3.S3FileIO","client.region":"us-east-1"}}

Defensive patterns

Strategy: try-catch

Validate before calling

// preflight checks before building the catalog
assertProp(catalogProperties, "warehouse");
assertProp(catalogProperties, "io-impl");
assertProp(catalogProperties, "client.region");
if (System.getenv("AWS_REGION") == null
    && System.getProperty("aws.region") == null
    && catalogProperties.getProperty("client.region") == null) {
  throw new IllegalStateException("AWS region must be set for Glue catalog");
}

Try / catch

try {
  catalog = createGlueCatalog(catalogProperties);
} catch (RuntimeException e) {
  if (e.getMessage().contains("Failed to initialize Glue catalog")) {
    // inspect e.getCause(): missing prop, NoClassDefFoundError (SDK),
    // credentials/region failure, or connectivity — remediate accordingly
  } else {
    throw e;
  }
}

Prevention

Always set warehouse, io-impl, and AWS region in catalogProperties for the glue catalog type.
Ensure the AWS SDK jars ship with the druid-iceberg-extensions load spec and verify with a smoke test at startup.
Grant the Druid task/instance IAM role glue:GetDatabase, glue:GetTable, and S3 access to the warehouse bucket.
Log and inspect the wrapped cause immediately — 'Failed to initialize Glue catalog' is only the wrapper, never the root cause.
Validate network access to glue.<region>.amazonaws.com (VPC endpoints, proxy settings) before deployment.

When it happens

Trigger: Creating an Iceberg input source with type=glue when: catalogProperties lack required keys (e.g. warehouse, io-impl, AWS region), the AWS SDK cannot build a Glue client, the JVM context-classloader swap reveals missing AWS SDK dependencies, or the Glue endpoint is unreachable during initialize().

Common situations: Missing or invalid druid.iceberg.catalog properties (no warehouse location or region configured); absent or expired AWS credentials in the environment/IAM role; wrong or unset AWS region; GlueCatalog class/dependency version conflicts in the extension classpath; network/proxy blocking the Glue endpoint; insufficient IAM permissions (glue:* on the target catalog).

Related errors

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/b748d60fe79d217e. Report an issue: GitHub.