ha-handler/lib/ha_handler/control.ex

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Elixir
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defmodule HAHandler.Control do
@moduledoc """
This module handles the decision-logic and actions to be
taken regarding the current state of the infrastructure.
"""
@haproxy_pgsql_backend "pgsql"
use GenServer
require Logger
alias HAHandler.{PGSQL, HAProxy}
# How much do we wait (ms) between each check/decision-making round?
@refresh 15_000
def start_link(opts) do
GenServer.start_link(__MODULE__, opts, name: __MODULE__)
end
@impl true
def init(_opts) do
state = []
# Let's skip the initial startup round so that other components are all up
# and running.
Process.send_after(self(), :sync, @refresh)
{:ok, state}
end
@impl true
def handle_info(:sync, state) do
Logger.debug("Executing control logic.")
# Fetch PGSQL state, make sure HAProxy routes to the master
# process.
pgsql_state =
PGSQL.get_instances()
|> Enum.map(fn {hostname, pid} = instance ->
haproxy_server =
HAHandler.pgsql_instances()
|> Enum.filter(fn opts -> Keyword.get(opts, :hostname) == hostname end)
|> Enum.at(0)
|> Keyword.get(:haproxy_server)
%{
haproxy_server: haproxy_server,
pgsql_watcher_pid: pid,
pgsql_operation_mode: PGSQL.get_operation_mode(instance)
}
end)
haproxy_state =
HAProxy.get_stats()
|> Map.get("Server", [])
|> Enum.filter(fn mapping -> mapping["pxname"] == @haproxy_pgsql_backend end)
|> Enum.map(fn mapping -> %{mapping["svname"] => mapping["status"]} end)
|> Enum.reduce(&Map.merge/2)
for pgsql_instance <- pgsql_state do
haproxy_state = Map.get(haproxy_state, pgsql_instance.haproxy_server)
case {pgsql_instance.pgsql_operation_mode, haproxy_state} do
{:primary, "UP"} ->
:noop
{:primary, "MAINT"} ->
Logger.info("Enabling routing PGSQL to (now) primary #{pgsql_instance.haproxy_server}.")
HAProxy.set_server(
@haproxy_pgsql_backend,
pgsql_instance.haproxy_server,
"state",
"ready"
)
{:secondary, "UP"} ->
Logger.info(
"Disabling routing PGSQL to (now) secondary #{pgsql_instance.haproxy_server}."
)
HAProxy.set_server(
@haproxy_pgsql_backend,
pgsql_instance.haproxy_server,
"state",
"maint"
)
{:secondary, "MAINT"} ->
:noop
unknown ->
Logger.warning("Unhandled PGSQL/HAProxy state: #{inspect(unknown)}")
end
end
# Schedule next round.
Process.send_after(self(), :sync, @refresh)
{:noreply, state}
end
end