To be honest, I don’t exactly how but I removed everything and I start the hole process again from the bottom but with “db” as host name and not “localhost”.
It make sense. There is no database in ojs container so moving from “localhost” to “db” could fix it.
Replacing “ojsPwd” by “ojs” fix the problem and the error is gone.
Hurray!! We are closer now. 
I am getting another one “The directory specified for uploaded files does not exist or is not writable.”
When working with docker you need to think who is asking you about an error.
At the beginning could be confusing, but you will get the logic so fast.
Remember this: Think in containers as independent machines with the application you are running. This is the magic of docker… your application is independent of the host that runs docker, so you won’t never have conflicts with libraries, or a mess of logs, etc.
In this case, as you are running the installer, the “ojs” container is the one that is talking you you need to specify a path inside the container.
The container is a linux machine, so it won’t never be something as “C:/whatever” it will be “/whatever”.
And the right path depends on how you define the volumes… and if no volume is created, the default will be “/var/www/files”.
Checking the docker-compose.yml you sent, in the volumes of your “ojs” container looks like you are not using volumes so try with using the default path (/var/www/files).
I don’t know what are you going to do with project, but remember what I explained before about “persistency” in docker": by default, all stuff is volatile and will be “reset” on every run, so “volumes” are there to store all the data that you like to be persistent.
If you like to create a volume for your uploaded files, you need to go to docker-compose.yml and uncomment this line before you run your installation:
- ./volumes/private:/var/www/files
This is what is done by default in ojs docker-compose.yml for the database data… because I can’t imagine an scenario where you don’t want your database persistent.
So, summarizing:
- Try it without container, just setting your upload folder to “/var/www/files”.
- If i works, stop with “docker-compose stop” and uncomment docker-compose.yml to use a volume for private data (as explained before).
Cheers,
m.