# Runtime troubleshooting

This page describes runtime errors that are not covered by [Performance troubleshooting](<../performance-troubleshooting/index.md>) and how to resolve them.

## CycloneDDS: Failed to find a free participant index

### Symptoms

When running Autoware on **ROS 2 Jazzy** (Ubuntu 24.04) with `RMW_IMPLEMENTATION=rmw_cyclonedds_cpp`, some nodes fail to start with errors such as:

```text
[component_container_mt-16] Failed to find a free participant index for domain 0
[component_container_mt-16] [ERROR] [rmw_cyclonedds_cpp]: rmw_create_node: failed to create domain, error Error (check_create_domain() at ./src/rmw_node.cpp:1242)
[component_container_mt-16] terminate called after throwing an instance of 'rclcpp::exceptions::RCLError'
[component_container_mt-16]   what():  failed to initialize rcl node: error not set, at ./src/rcl/node.c:252
```

This often occurs when launching demos that use many nodes (e.g. [Planning simulation](<../../../../simulation/planning-simulation/index.md>)).

### Cause

CycloneDDS itself defaults to `ParticipantIndex=none`, which does not limit the number of participants. However, on ROS 2 Jazzy, **rmw\_cyclonedds\_cpp** builds the domain configuration and explicitly sets `ParticipantIndex=auto` and `MaxAutoParticipantIndex=32`, overriding the CycloneDDS default. As a result, only about 32 DDS participants can exist per host. Autoware can use more DDS participants than this limit (e.g. 100 or more), so new nodes cannot obtain a free participant index and fail to create the domain.

This behavior comes from the RMW implementation. See [rmw\_cyclonedds: check\_create\_domain()](<https://github.com/ros2/rmw_cyclonedds/blob/7cd457de5825d4cb46ec7b081aa00a5392e388d0/rmw_cyclonedds_cpp/src/rmw_node.cpp#L1193-L1199>) (lines 1193–1199).

### Solution

Configure CycloneDDS by adding a `<Discovery>` section to your `cyclonedds.xml` with `ParticipantIndex` set to `none`:

```xml
<Discovery>
  <ParticipantIndex>none</ParticipantIndex>
</Discovery>
```

A full example is given in [CycloneDDS Configuration](<../../../../installation/additional-settings-for-developers/network-configuration/dds-settings/#cyclonedds-configuration>).

### References

- [autowarefoundation/autoware\#6759](<https://github.com/autowarefoundation/autoware/issues/6759>): Issue and discussion for this error
- [rmw\_cyclonedds: check\_create\_domain() (ParticipantIndex=auto, MaxAutoParticipantIndex=32)](<https://github.com/ros2/rmw_cyclonedds/blob/7cd457de5825d4cb46ec7b081aa00a5392e388d0/rmw_cyclonedds_cpp/src/rmw_node.cpp#L1193-L1199>): Where the RMW overrides CycloneDDS defaults
- [Eclipse Cyclone DDS: Controlling port numbers](<https://cyclonedds.io/docs/cyclonedds/0.9.1/config.html#controlling-port-numbers>)
- [CycloneDDS config reference: MaxAutoParticipantIndex](<https://cyclonedds.io/docs/cyclonedds/latest/config/config_file_reference.html#cyclonedds-domain-discovery-maxautoparticipantindex>)