apache/beam · error · RuntimeException

Unable to create the keytab file for the provided secret.

Error message

Unable to create the keytab file for the provided secret.

What it means

While rewriting keytab secret references in sasl.jaas.config, processSecret() matches each secret reference and requires a non-empty captured secret ID. If the regex matched but group(1) is null or empty, it throws this RuntimeException, since it cannot resolve a secret for an empty identifier.

Source

Thrown at sdks/java/extensions/kafka-factories/src/main/java/org/apache/beam/sdk/extensions/kafka/factories/KerberosConsumerFactoryFn.java:141

        // a keytab file and overwrite it.
        continue;
      }
      String filename = "kafka-client-" + UUID.randomUUID().toString() + ".keytab";

      localFileString = super.getBaseDirectory() + "/" + LOCAL_FACTORY_TYPE + "/" + filename;
      Path localFilePath = Paths.get(localFileString);
      Path parentDir = localFilePath.getParent();
      try {
        if (parentDir != null) {
          Files.createDirectories(parentDir);
        }
        Files.write(localFilePath, secretValue);
        if (!new File(localFileString).canRead()) {
          LOG.warn("The file is not readable");
        }
        LOG.info("Successfully wrote file to path: {}", localFilePath);
      } catch (IOException e) {
        throw new RuntimeException("Unable to create the keytab file for the provided secret.");
      }
    }
    // if no localFile was created, then we can assume that the secret is meant to be kept as a
    // value.
    return localFileString.isEmpty()
        ? new String(secretValue, StandardCharsets.UTF_8)
        : localFileString;
  }
}

View on GitHub (pinned to 12126d8942)

Solutions

Inspect the sasl.jaas.config value and fix the incomplete secret reference so the captured secret ID is non-empty
Ensure template substitution ran before the pipeline consumed the config
Validate the secret reference format (prefix + non-empty ID) in a pre-launch config check
Escape/avoid literal occurrences of the secret prefix pattern in unrelated values

Example fix

// before
keyTab="${KEYTAB_SECRET}"   // substituted to empty
// after
keyTab="gs://my-bucket/secrets/krb5.keytab"  // non-empty secret reference

Defensive patterns

Strategy: try-catch

Validate before calling

java
Path dir = Paths.get(localKeytabDir);
if (!Files.isDirectory(dir) || !Files.isWritable(dir)) {
  throw new IllegalStateException("Keytab directory missing or not writable: " + dir);
}

Try / catch

java
try {
  factoryFn.processSecret(config);
} catch (RuntimeException ex) {
  if (ex.getMessage().startsWith("Unable to create the keytab file")) {
    log.severe("Keytab write failed — check worker FS permissions/disk (cause not chained)");
  }
}

Prevention

Pre-create a writable staging directory in the worker image
Ensure containers run with a writable /tmp or designated keytab dir
Monitor disk space on workers
Instrument Files.write with your own try/catch to capture the real IOException

When it happens

Trigger: sasl.jaas.config contains a keytab secret reference whose captured group is empty — e.g. a dangling prefix like "gs://" or an empty ${...}/secret placeholder produced by templating.

Common situations: Config templating left an empty variable; hand-edited sasl.jaas.config with a truncated secret URL; regex-matching a prefix pattern in a value that was never fully substituted.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/0e819f55feaf9cdd. Report an issue: GitHub.