Is it possible to control which port the mackerel-agent uses? While it's not possible to control the port, we do support connection via proxy. For more information please refer to the section "I want to connect via HTTP Proxy." in the agent specs. Related articles How do the Mackerel and the mackerel-agent communicate? What is the time interval between alert checks? What kind of configuration is Mackerel's connectivity monitoring working with? The agent won’t startup. Calculating the number of hosts