| Note: This tutorial assumes that you have completed the previous tutorials: Redis Debugging. |
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Launching a Gateway Hub
Description: Launching and connecting to a Gateway HubKeywords: multimaster, gateway, hub
Tutorial Level: BEGINNER
Next Tutorial: Command Line Tools
Contents
Overview
The relevant launchers are all nicknamed buccaneer_xxx.launch in this package. Take particular note of the parameters configured in each.
Launching Configurations
Static Ip/Hostname
The most minimalistic way to start a hub/gateway - preconfiguring via parameters.
You'll note that the hub has a parameter controlling which port the redis server should start on. The gateway also has a parameter configuring the uri where it can find the redis server.
# 1st Shell > roslaunch --port=11311 rocon_gateway_tutorials buccaneer_hub.launch # 2nd Shell > roslaunch --port=11312 rocon_gateway_tutorials buccaneer_gateway_param.launch
Ros Services
Sometimes the gateway uri is not known at startup. In which case the gateway can delay its connection to the hub until the hub uri (redis uri) is known.
# 1st Shell > roslaunch --port=11311 rocon_gateway_tutorials buccaneer_hub.launch # 2nd Shell > roslaunch --port=11312 rocon_gateway_tutorials buccaneer_gateway_ros_api.launch # 3rd Shell > export ROS_MASTER_URI=http://localhost:11312 > rosrun rocon_gateway_tutorials connect_localhost.py
The script connect_localhost.py simply calls the connect_hub service with the required parameters.
Zeroconf
Lastly, you can use zeroconf to auto-discover the hub's uri and automatically connect.
# 1st Shell > roslaunch --port=11311 rocon_gateway_tutorials buccaneer_hub.launch # 2nd Shell > roslaunch --port=11312 rocon_gateway_tutorials buccaneer_gateway_zeroconf.launch
Selective Connections
Gateways typically connect to the first auto-discovered hub or first configured hub (either by param or ros api). They can be configured to selectively filter or choose a particular hub via the hub's name parameter and the gateways' hub_whitelist and hub_blacklist arrays.
All of the previous buccaneer launchers specifically set the hub name to Bucanneer Hub and also insert the same name into each gateway's hub_whitelist array.
# In the hub launcher
<rosparam param="name">Buccaneer Hub</rosparam>
# In the gateway launcher
<rosparam param="hub_whitelist">['Buccaneer Hub']</rosparam>