Manages TTL health check workers used by mesh services.

Consul agent can use multiple kinds of checks, e.g. script checks, HTTP and TCP checks, gRPC and others.

MeshxConsul is using TTL (Time To Live) health checks for services started with MeshxConsul.start/4. Dedicated worker is used to periodically update service health check state over Consul agent HTTP interface.

Service health checks are defined using template argument of MeshxConsul.start/4. Default health check specification:

[
  ttl: %{
    id: "ttl:{{id}}",
    status: "passing",
    ttl: 5_000
  }
]

Health check keys:

• :id - service id (value rendered using Mustache system),
• :status - initial health check status,
• :ttl - health check state update interval, milliseconds.

Health check state can be one of following: "passing", "warning" or "critical".

TTL checks are automatically started when running MeshxConsul.start/4 and stopped with MeshxConsul.stop/1. Users usually should not directly use start/2 and stop/1 functions defined in this module.

set_status/2 can be used to set service status depending on external conditions. One can for example use :os_mon :cpu_sup to monitor CPU utilization and update service status accordingly.

Example:

iex(1)> MeshxConsul.start("service1")
{:ok, "service1-h11", {:tcp, {127, 0, 0, 1}, 1024}}
iex(2)> MeshxConsul.Ttl.get_status("service1-h11")
"passing"
iex(3)> MeshxConsul.Ttl.set_status("service1-h11", "warning")
:ok
iex(4)> MeshxConsul.Ttl.get_status("service1-h11")
"warning"