1. Caddy version (caddy version):
2.4.5
2. How I run Caddy:
a. System environment:
Docker via docker-compose. Ubuntu 21.04
b. Command:
docker-compose up
c. Service/unit/compose file:
version: '3.3'
services:
caddy:
container_name: caddy
build: ./caddy
ports:
- "80:80"
- "443:443"
- "80:80/udp"
- "443:443/udp"
volumes:
- ${CONFIG_PATH}/caddy/Caddyfile:/etc/caddy/Caddyfile
- ${CONFIG_PATH}/var/caddy:/root/.caddy
- ${CONFIG_PATH}/caddy/data:/data
- ${CONFIG_PATH}/caddy/config:/config
# BEGIN SECTION THAT IS CAUSING PROBLEMS -----------------
- ${WWW_PATH}/${HOST_1}:/var/www/html**
- ${WWW_PATH}/${HOST_2}:/var/www/html**
# END SECTION THAT IS CAUSING PROBLEMS -------------------
restart: always
wp1:
# build: .
image: wordpress:fpm-alpine
container_name: ${HOST_1}-wp
hostname: $SITE_1
networks:
- $DEFAULT_NETWORK
depends_on:
- db1
environment:
WORDPRESS_DB_PASSWORD: $DB_PASSWORD
WORDPRESS_DB_HOST: db1
WORDPRESS_DB_USER: $DB_USER
WORDPRESS_DB_NAME: $DB_NAME
volumes:
- ${WWW_PATH}/${HOST_1}:/var/www/html
restart: always
db1:
image: $DB_IMAGE
container_name: ${HOST_1}-wp-db
networks:
- $DEFAULT_NETWORK
environment:
MYSQL_RANDOM_ROOT_PASSWORD: '1'
MYSQL_USER: $DB_USER
MYSQL_PASSWORD: $DB_PASSWORD
MYSQL_DATABASE: $DB_NAME
volumes:
- ${CONFIG_PATH}/mysql/${HOST_1}:/var/lib/mysql
restart: always
wp2:
# build: .
image: wordpress:fpm-alpine
container_name: ${HOST_2}-wp
hostname: $SITE_2
networks:
- $DEFAULT_NETWORK
depends_on:
- db2
environment:
WORDPRESS_DB_PASSWORD: $DB_PASSWORD
WORDPRESS_DB_HOST: db2
WORDPRESS_DB_USER: $DB_USER
WORDPRESS_DB_NAME: $DB_NAME
volumes:
- ${WWW_PATH}/${HOST_2}:/var/www/html
restart: always
db2:
image: $DB_IMAGE
container_name: ${HOST_2}-wp-db
networks:
- $DEFAULT_NETWORK
environment:
MYSQL_RANDOM_ROOT_PASSWORD: '1'
MYSQL_USER: $DB_USER
MYSQL_PASSWORD: $DB_PASSWORD
MYSQL_DATABASE: $DB_NAME
volumes:
- ${CONFIG_PATH}/mysql/${HOST_2}:/var/lib/mysql
restart: always
d. My complete Caddyfile or JSON config:
{$SITE_1} {
root * /var/www/html
php_fastcgi {$DOCKER_HOST_1}:{$FPM_PORT}
file_server
}
{$SITE_2} {
root * /var/www/html
php_fastcgi {$DOCKER_HOST_2}:{$FPM_PORT}
file_server
}
3. The problem I’m having:
TL;DR: Can’t get multiple Wordpress Docker instances to function if using -fpm versions
When using php-fpm, Caddy points to the same volume mapping (/var/www/html) in docker-compose.yml. When defining the Caddy service in compose, specifying different source volumes does not give it anything to distinguish the target volume since it is the same.
Is there a clean way to use the official Wordpress fpm images with docker-compose, and tell Caddy that the var/www/html paths are in different containers? 
4. Error messages and/or full log output:
No error message. It just serves the same root directory for all domains specified in Caddy
5. What I already tried:
This works fine if I use regular WP (not PHP-FPM).
PHP-FPM works if I build unique containers with unique tags, then change the target volume path inside the container. For instance, if the containers’ /var/www/html paths are internally renamed to /var/ww1/html and /var/ww2/html, I can provide the caddy service volume mapping which looks like this:
# - ${WWW_PATH}/${HOST_1}:/var/www1/html
# - ${WWW_PATH}/${HOST_2}:/var/www2/html
Requiring a separate container build for each WP service feels super kludgy. And in benchmarks, PHP-FPM seems to be significantly faster (in the ballpark of 300%).
6. Links to relevant resources:
My earlier thread on Docker / WP configs