apache/cassandra · error · IllegalArgumentException

Cannot set source data center to be local data center, when

Error message

Cannot set source data center to be local data center, when excludeLocalDataCenter flag is set

What it means

rebuild validates that when the --exclude-local-datacenter flag is set, the chosen source DC must not equal the local data center, since excluding local DC nodes leaves no possible sources if the source is the local DC itself.

Source

Thrown at src/java/org/apache/cassandra/service/Rebuild.java:86

    @VisibleForTesting
    public static void unsafeResetRebuilding()
    {
        isRebuilding.set(false);
    }

    public static void rebuild(String sourceDc, String keyspace, String tokens, String specificSources, boolean excludeLocalDatacenterNodes)
    {
        // check ongoing rebuild
        if (!isRebuilding.compareAndSet(false, true))
        {
            throw new IllegalStateException("Node is still rebuilding. Check nodetool netstats.");
        }

        if (sourceDc != null)
        {
            if (sourceDc.equals(DatabaseDescriptor.getLocalDataCenter()) && excludeLocalDatacenterNodes) // fail if source DC is local and --exclude-local-dc is set
                throw new IllegalArgumentException("Cannot set source data center to be local data center, when excludeLocalDataCenter flag is set");
            Set<String> availableDCs = ClusterMetadata.current().directory.knownDatacenters();
            if (!availableDCs.contains(sourceDc))
            {
                throw new IllegalArgumentException(String.format("Provided datacenter '%s' is not a valid datacenter, available datacenters are: %s",
                                                                 sourceDc, String.join(",", availableDCs)));
            }
        }

        try
        {
            // check the arguments
            if (keyspace == null && tokens != null)
            {
                throw new IllegalArgumentException("Cannot specify tokens without keyspace.");
            }

            logger.info("rebuild from dc: {}, {}, {}", sourceDc == null ? "(any dc)" : sourceDc,
                        keyspace == null ? "(All keyspaces)" : keyspace,

View on GitHub (pinned to 88fd0f6a0e)

Solutions

Omit the sourceDc argument so rebuild picks a non-local DC automatically
Pass a source DC different from the local data center
Remove the --exclude-local-datacenter flag if streaming from the local DC is actually intended

Example fix

// before
nodetool rebuild --exlude-local-dc dc1
dc1
// after (source must differ from local DC)
nodetool rebuild -- dc2

Defensive patterns

Strategy: validation

Validate before calling

String local = DatabaseDescriptor.getLocalDataCenter();
if (excludeLocalDc && sourceDc != null && sourceDc.equals(local))
    throw new IllegalArgumentException("sourceDc must differ from local DC when excludeLocalDatacenterNodes=true");

Try / catch

try { rebuild(sourceDc, ..., true); } catch (IllegalArgumentException e) { if (e.getMessage().contains("excludeLocalDataCenter")) rebuild(null, ...); else throw e; }

Prevention

Never combine --exclude-local-datacenter with an explicit source DC equal to the local DC
Verify cassandra-rackdc.properties local_dc value matches the DC name you pass
Prefer omitting sourceDc and letting rebuild pick a remote DC automatically

When it happens

Trigger: Calling rebuild(sourceDc=X, ..., excludeLocalDatacenterNodes=true) where X equals DatabaseDescriptor.getLocalDataCenter().

Common situations: Operator runs `nodetool rebuild --exlude-local-dc` (or -dl) and still passes the local DC as source; copy-pasted runbook command with wrong DC name; misconfigured local data center in cassandra-rackdc.properties so the 'remote' DC name matches local.

Understand the failure class

Background: Conflicting config options: "cannot be used together" — configuration validation errors across open-source libraries — this error's family across 162 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/39a5ca8b18fcce70. Report an issue: GitHub.