apache/hadoop · error · IllegalArgumentException

Not allow to remove an inner node: {}

Error message

Not allow to remove an inner node: {}

What it means

NetworkTopology.remove(Node) removes only leaf nodes. Inner nodes (racks/switches) are structural: their counters (numOfRacks, empty-rack bookkeeping) are updated by removing their leaves, so removing an InnerNode directly is rejected with IllegalArgumentException before the write lock is taken.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/NetworkTopology.java:224

      if (!NodeBase.ROOT.equals(loc)) {
        loc = loc.substring(1);
      }
      InnerNode rack = (InnerNode) clusterMap.getLoc(loc);
      return (rack == null) ? new ArrayList<>(0)
          : new ArrayList<>(rack.getChildren());
    } finally {
      netlock.readLock().unlock();
    }
  }

  /** Remove a node
   * Update node counter and rack counter if necessary
   * @param node node to be removed; can be null
   */ 
  public void remove(Node node) {
    if (node==null) return;
    if( node instanceof InnerNode ) {
      throw new IllegalArgumentException(
        "Not allow to remove an inner node: "+NodeBase.getPath(node));
    }
    LOG.info("Removing a node: "+NodeBase.getPath(node));
    netlock.writeLock().lock();
    try {
      if (clusterMap.remove(node)) {
        InnerNode rack = (InnerNode)getNode(node.getNetworkLocation());
        if (rack == null) {
          numOfRacks--;
        }
        interRemoveNodeWithEmptyRack(node);
      }
      LOG.debug("NetworkTopology became:\n{}", this);
    } finally {
      netlock.writeLock().unlock();
    }
  }

View on GitHub (pinned to 2add963021)

Solutions

1. Remove each leaf under the rack instead of the rack itself — the rack disappears automatically when its last leaf is removed
2. Filter nodes with !(node instanceof InnerNode) before calling remove()
3. To reset the whole map, rebuild the topology object rather than removing inner nodes

Example fix

// before
topology.remove(nodeFromLookup); // may be an InnerNode

// after
if (!(nodeFromLookup instanceof InnerNode)) {
  topology.remove(nodeFromLookup);
}

if (node instanceof InnerNode) {
  throw new IllegalArgumentException(
      "Refusing to remove inner node " + NodeBase.getPath(node));
}
topology.remove(node);

static boolean isRemovableLeaf(Node n) {
  return n != null && !(n instanceof InnerNode);
}

When it happens

Trigger: Calling remove(node) where node instanceof InnerNode — e.g. a node obtained from getNode(path)/getDatanodesInRack() that is actually a rack, or a test stub extending InnerNode.

Common situations: Decommissioning or cluster-drain tooling that fetches nodes by path and removes them without a type check; unit tests with mock nodes extending InnerNodeImpl.

Related errors

• Not allow to add an inner node: {}
• Network Locationpath doesn't start with /: {}
• Not allow to add an inner node: {}
• Not allow to remove an inner node: {}
• Network location name contains /: {}

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/93655fee611deec1. Report an issue: GitHub.