load_module /usr/lib/nginx/modules/ndk_http_module.so;
load_module /usr/lib/nginx/modules/ngx_http_lua_module.so;

http {
    lua_shared_dict state 12k;
    init_by_lua_block {
        ngx.shared.state:set("suspend", false)
    }
    # rest of your http block
}

location = /suspend/MySuperSecretMagicString {
    if ($request_method = PUT) {
        content_by_lua_block {
            ngx.req.read_body()
            content = ngx.req.get_body_data()
            if (content == "go2sleep") then
                ngx.shared.state:set("suspend", true)
            else
                ngx.shared.state:set("suspend", false)
            end
        }
    }
}

location / {
    access_by_lua_block {
        while (ngx.shared.state:get("suspend") == true) do
            ngx.sleep(0.2)
        end
    }
    proxy_pass http://my-backend;
}

curl -X PUT -d go2sleep http://localhost/suspend/MySuperSecretMagicString

curl -X PUT -d UnleashTheHounds http://localhost/suspend/MySuperSecretMagicString