Check the server log

shifter_local is using the two containers to run WordPress. You need to get shifter-local_wp container like this command.

$ docker ps | grep shifter-local_wp
0cd71f3f03a3        getshifter/shifter_local:latest   "/init.alpine"           11 days ago         Up 11 days          9000/tcp, 0.0.0.0:8443->443/tcp   shifter-local_wp_1

In this example, 0cd71f3f03a3 is the target container id.

After that, you can check the server log by docker log command like this.

$ docker logs 0cd71f3f03a3 -f
127.0.0.1:8443 172.18.0.1 - 200 POST HTTP/2 /wp-admin/admin-ajax.php 47 0.002390 0.107255
127.0.0.1:8443 172.18.0.1 - 200 POST HTTP/2 /wp-admin/admin-ajax.php 47 0.003582 0.122187
127.0.0.1:8443 172.18.0.1 - 200 POST HTTP/2 /wp-admin/admin-ajax.php 47 8.007719 0.139107
127.0.0.1:8443 172.18.0.1 - 200 POST HTTP/2 /wp-admin/admin-ajax.php 47 0.002795 0.119853