I found a solution myself!
I deleted the /data folder where all the custom data for the synapse docker container is located, in my case /docker_data/synapse-data.
I have modified the docker-comose file as follows, the main change concerns the network setting:
version: "3.3"
services:
synapse:
image: "matrixdotorg/synapse:latest"
container_name: "synapse"
volumes:
- /docker_data/synapse-data:/data
environment:
TZ: DE
VIRTUAL_HOST: "matrix.my_own.duckdns.org"
VIRTUAL_PORT: 8008
LETSENCRYPT_HOST: "matrix.my_own.duckdns.org"
SYNAPSE_SERVER_NAME: "matrix.my_own.duckdns.org"
SYNAPSE_REPORT_STATS: "yes"
restart: always
networks: ["swag_default"]
networks:
swag_default:
external: true
In the swag configuration nginx/proxy-confs I have renamed the synapse.subdomain.conf.sample to synapse.subdomain.conf without changes. After that I restarted swag.
I did the initial configuration of synapse with the following command.
docker-compose run --rm synapse generate
In the homeserver.yaml I verified that the server name is stored correctly and that TLS is deactivated.
Finally, I started the synapse server with the docker-compose up -d command.
If the following image appears after calling https://matrix.my_own.duckdns.org in the browser, everything works.
Depending on the setting of the homserver.yaml file, new USERs must be created manually, this can be done by using the command docker exec -it synapse register_new_matrix_user http://localhost:8008 -c /data/homeserver.yaml.