Communicator enables you to pass messages to Agents, Workers and Tests. You can use messages to simulate various conditions: for example, Hazelcast discomforts like network partitioning and high CPU utilization.


$ communicator --message-address Agent=*,Worker=* spinCore

This will send the message spinCore to all Workers.

Each interaction with Communicator has to specify:

  • Message Type
  • Message Address

Message Types

  • kill - Kills a JVM running a message recipient. In practice, you probably want to send this message to Worker(s) only. The reason for this is you rarely want to kill an Agent and it does not make sense to send this to just a single test; it would kill other tests sharing the same JVM as well.
  • blockHzTraffic - Blocks the incoming traffic to TCP port range 5700:5800.
  • newMember - Starts a new member. You can send this message to Agents only.
  • softKill - Instructs a JVM that is running a message recipient to exit.
  • spinCore - Starts a new busy-spinning thread. You can use it to simulate increased CPU consumption.
  • unblockTraffic - Open ports blocked by the blockHzTraffic message.
  • oom - Forces a message recipient to use all memory and cause an OutOfMemoryError.
  • terminateWorker - Terminates a random Worker. This message type can be targeted to an Agent only.

Message Addressing

You can send a message to Agent, Worker or Test. These resources create a naturally hierarchy, making the messaging address hierarchical as well.

Syntax: Agent=<mode>[,Worker=<mode>[,Test=<mode>]].

Mode can be either '*' for broadcast or 'R' for a single random destination.

Addressing Example 1:

Agent=*,Worker=R: A message will be routed to all agents, then each agent will pass it to a single random worker, and each worker will pass the message for processing.

Addressing Example 2:

Agent=*,Worker=R,Test=*: A message will be routed to all agents, then each agent will pass the message to a single random worker and workers will pass the message to all tests for processing.

Addressing shortcuts

Hierarchical addressing is powerful, but it can be quite verbose. You can use convenient shortcuts, as shown below.

  • --oldest-member: Sends a message to a worker with the oldest cluster member.
  • --random-agent: Sends a message to a random agent.
  • --random-worker: Sends a message to a random worker.

Example: The following command starts a busy-spinning thread in a JVM running a random Worker.

communicator --random-worker spinCore