Introducing the sps_filesync gem

To sync a file between 2 different nodes you will need to set up the following:

• an SPS broker to publish to the subscriber that a file has been written, copied, move, or removed
• a DRb_fileserver_plus service which acts like a DRB_fileserver, is fault tolerant to node failure and publishes an SPS message to the SPS broker whenever a file is modified
• a DRb_filesync service to listen for file changes and perform the same file operation on each of the other nodes
• a DRb_fileserver for each node
• a node (machine) containing a copy of the file directory from the other node.

require 'simplepubsub'

SimplePubSub::Broker.start port: '59000'

Ensure the service is started in the directory containing the files to be synchronised.

require 'drb_fileserver'

DRbFileServer.new(host: '0.0.0.0').start

Ensure the service is started in the directory containing a copy of the files from node 1.

require 'drb_fileserver'

DRbFileServer.new(host: '0.0.0.0').start

This can be run on any box and it is recommended it doesn't run on the same box as either node 1 or node 2 to avoid port conflicts.

# host used in this example is 192.168.4.135

require 'sps_filesync'

SpsFileSync.new(['192.168.4.177', '192.168.4.20'], host: 'sps').subscribe

Note: All available nodes should be added to the list, including the master node as the service will identify using the SPS message payload which node is the master.

Using the DRb_fileserver_plus service as the DRb fileserver write "hello world" to a file called hello.txt.

require 'drb_fileclient'

DfsFile.write('dfs://192.168.4.135/hello.txt', 'hello world')

• A file called hello.txt should now be observed in both nodes 1 (192.168.4.177) and 2 (192.168.4.20).

The diagram below illustrates the flow of messages throughout the different stages of writing and syncronising files.

Note: At stage 2 where the file is written, both steps 3 and 4 are triggered at once since they are independent of each other.

• sps_filesync https://rubygems.org/gems/sps_filesync

drb_filesync gem drb sps fileserver server service sync