Comment 7 for bug 2046877

"amphora configure" doesn't work because:

- CONF.mutate_config_file() is called in the API server [0]
- CONF.health_manager.heartbeat_key is read [1] in another process [2]

to fix it we need to call CONF.mutate_config_file() at the beginning of the _send_msg function [3], it reloads the config files and updates only the mutable settings.

[0] https://opendev.org/openstack/octavia/src/commit/240b0066a12fc81c9e42aade67435cbb0e65c2a5/octavia/amphorae/backends/agent/api_server/server.py#L247
[1] https://opendev.org/openstack/octavia/src/commit/240b0066a12fc81c9e42aade67435cbb0e65c2a5/octavia/amphorae/backends/health_daemon/health_sender.py#L51
[2] https://opendev.org/openstack/octavia/src/commit/240b0066a12fc81c9e42aade67435cbb0e65c2a5/octavia/cmd/agent.py#L59-L63
[3] https://opendev.org/openstack/octavia/src/commit/240b0066a12fc81c9e42aade67435cbb0e65c2a5/octavia/amphorae/backends/health_daemon/health_sender.py#L49