Deploying Traefik with LetsEncrypt and multiple Docker backend - traefik

Question

I am considering replacing Apache for Traefik for my web project (Kestrel / .Net Core). After reading the documentation, a few things remain unclear to me regarding Traefik:
1/ Does Traefik automatically handle the LetsEncrypt certificate renewal or does it need to be done manually or via an external script? From the doc it's said that this is performed when adding a new host or restart, but what happens after 3 months of Traefik running without any restart/new host added?
2/ When a Docker backend becomes unreachable, how is it possible to serve a custom static HTML page? I can see how to set specific error page from the documentation, but not how to redirect trafic to it when a given backend becomes unavailable.
3/ When a Docker backend needs to be updated, is there some steps that need to be performed on Traefik prior to performing the Docker stop/restart?
4/ It seems I can't get to have 2 docker backend running at the same time, see the configuration file below, if I uncomment the 2nd backend (api.mydomain.io), then the 1st one becomes not available anymore. Am I missing something here?
version: '3'
services:
reverse-proxy:
image: traefik # The official Traefik docker image
command: --docker # Enables the web UI and tells Træfik to listen to docker
ports:
- "80:80" # The HTTP port
- "443:443" # The HTTPS port
- "8080:8080" # The Web UI (enabled by --api)
networks:
- proxy
volumes:
- /var/run/docker.sock:/var/run/docker.sock
- $PWD/traefik.toml:/etc/traefik/traefik.toml
- $PWD/acme.json:/acme.json
- /root/mydomain_prod/cert/:/certs/
- /root/mydomain_prod/503.html:/503.html
container_name: traefik-reverse-proxy
##############################
# Front - www.mydomain.io
##############################
mydomain-front:
image: mydomain-front
labels:
- traefik.enable=true
- traefik.backend=mydomain-front
- traefik.frontend.rule=Host:traefik.mydomain.io
- traefik.port=8084
networks:
- internal
- proxy
container_name: mydomain-front
##############################
# API - api.mydomain.io
# Note: If I uncomment this one, then www.mydomain.io won't work anymore
##############################
#mydomain-api:
# image: mydomain-api
# labels:
# - traefik.enable=true
# - traefik.backend=mydomain-api
# - traefik.frontend.rule=Host:api.mydomain.io
# - traefik.port=8082
# networks:
# - internal
# - proxy
# container_name: mydomain-api
Many thanks,
Flo

Answer 1

1/ Traefik can handle the LetsEncrypt certificate renewal. Just remember to create a Volume to store the acme.json file. When the certificate expires, Traefik will do the renewal without asking.
2/ I don’t know if it’s possible. If you find a solution, share it.
3/ When you need to update a Docker, just update it. Traefik will be trigger from that change and update is own configuration.
4/ You can have to backend running at the same time. Below you can see a docker-compose.yml configuration :
version: '3'
services:
two-backend-service:
restart: always
image: ……..
labels:
- traefik.enable=true
- traefik.service1.frontend.rule=Host:service1.exemple.com
- traefik.service1.frontend.passHostHeader=true
- traefik.service1.port=8082
- traefik.Service2.backend=service2
- traefik.Service2.frontend.rule=Host:service2.exemple.com
- traefik.Service2.frontend.passHostHeader=true
- traefik.Service2.port=8081
traefik:
build:
context: ./traefik
dockerfile: Dockerfile
restart: always
ports:
- 80:80
- 443:443
labels:
- traefik.enable=false
volumes:
- /var/run/docker.sock:/var/run/docker.sock:ro
- traefik_letsencrypt:/etc/traefik/acme/
volumes:
traefik_letsencrypt:
driver: local