ROS 2 across Docker containers: shared network, discovery and Fast DDS shared memory

contact@mulhamfetna.com (Mulham Fetna) — Wed, 16 Sep 2026 00:00:00 +0000

“The topic shows up in ros2 topic list, but echo prints nothing” — the classic ROS-in-Docker symptom. Here’s why it happens, how two containers in this project share a network and a block of memory instead, and what that costs.

How ROS 2 nodes find each other
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ROS 2 has no master. Nodes discover each other through DDS — in Jazzy, eProsima Fast DDS by default — using the SPDP protocol:

Each participant announces itself over UDP multicast (239.255.0.1) on ports derived from the domain ID \(d\): discovery multicast on \(7400 + 250d\), unicast on \(7410 + 250d + 2p\) for participant \(p\). For domain 42: UDP 17900 and 17910+.
Peers exchange their topic endpoints; matching publishers and subscribers connect.
Data flows over the best transport both support — shared memory when they share a host and /dev/shm, UDP otherwise.

Why Docker’s default network breaks it
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Compose attaches services to a bridge network — a private NATed subnet. Multicast isn’t reliably routed across it, and machines on your LAN can’t reach container IPs at all.

Networking on Mulham Fetna

ROS 2 across Docker containers: shared network, discovery and Fast DDS shared memory

How ROS 2 nodes find each other #

Why Docker’s default network breaks it #

How ROS 2 nodes find each other
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Why Docker’s default network breaks it
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