Macro http_upstream_init_peer_pt

macro_rules! http_upstream_init_peer_pt {
    ( $name: ident, $handler: expr ) => { ... };
}

Define a static upstream peer initializer

Initializes the upstream ‘get’, ‘free’, and ‘session’ callbacks and gives the module writer an opportunity to set custom data.

This macro will define the NGINX callback type: typedef ngx_int_t (*ngx_http_upstream_init_peer_pt)(ngx_http_request_t *r, ngx_http_upstream_srv_conf_t *us), we keep this macro name in-sync with its underlying NGINX type, this callback is required to initialize your peer.

Load Balancing: https://nginx.org/en/docs/dev/development_guide.html#http_load_balancing