this error seems to be caused by the fact that the ./db/bitcoin directory can't be created. I solved that by manually creating the directory inside the electrs folder. After that electrs could't access the auth-cookie in the bitcoin-node directory, because the permissions were jumbled. I fixed that by changing the permissions. annoyingly, the permissions are reset every time I restart the bitcoin docker. But even after all that electrs can't connect to the RPC service of bitcoind. No matter what I try, I get a "connection refused" error. I am at my wits end. And since there does not seem to be any kind of support here, I am ready to give up.
edit: I solved the last bit: The problem was, that the bitcoin RPC service is only listening on localhost by default. I couldn't figure out how to change that, unfortunately, because I couldn't figure out how to pass "-rpcallowip" when the docker starts. Instead, I changed the network to "host" in the settings of the bitcoin docker and the electrs docker. Now they are listening on the same IP and the localhost connection works. Now I only need to find a way to automatically change the permissions on the .cookie file each time the bitcoin docker restarts.#
Finally, I am not sure, if its a good idea to run v0.9 of electrs when 0.10.4 is already out.