Clustering nodes that are on different servers

[etranger7]

I'm using this docker image and trying to cluster 2 nodes that are on different servers, therefore 2 different public IPs.
Just for testing, I successfully clustered 2 docker containers that are on the same machine.

However, when I try to define a FQDN in ERLANG_NODE_ARG, I get an error that I don't know how to overcome.

This container starts without errors (I'm skipping unrelated lines):

services:
  ej1container:
    hostname: ej1container          # containername works here too
    environment:
      - ERLANG_NODE_ARG=ej1@ej1container

This setup gives me an error

services:
  ej1container:
    hostname: ej1container          # containername works here too
    environment:
      - ERLANG_NODE_ARG=ej1@subdomain.domain.com

It looks like the container starts normally but when I do

docker exec ej1container ejabberdctl status

I get

Failed RPC connection to the node 'ej1@subdomain.domain.com': nodedown

I already pointed the A record of subdomain.domain.com to the public IP of the VPS where this is running.

There was a similar issue #106 but I don't see how the FQDN was integrated and what the solution was.

Any help would be much appreciated.

[etranger7]

Update:
While the main node is running on Server A as ej1@ej1container, I tried to add Server B to it to form a cluster and ran into these issues:

• When I use A FQDN, I get

ej3con  | :> ejabberdctl join_cluster ej1@subdomain.domain.com
ej3con  | 
ej3con  | 21:31:47.574 [error] ** System NOT running to use fully qualified hostnames **
ej3con  | ** Hostname subdomain.domain.com is illegal **
ej3con  | 
ej3con  | Error: error
ej3con  | Error: "This node cannot reach that node."
ej3con  | :> FAILURE in command 'join_cluster ej1@subdomain.domain.com' !!! Stopping ejabberd...

• When I use an IP instead, I get

ej3con  | :> ejabberdctl join_cluster ej1@xxx.xxx.xxx.xx
ej3con  | 
ej3con  | 20:17:39.761 [error] ** System NOT running to use fully qualified hostnames **
ej3con  | ** Hostname xxx.xxx.xxx.xx is illegal **
ej3con  | 
ej3con  | Error: error
ej3con  | Error: "This node cannot reach that node."
ej3con  | :> FAILURE in command 'join_cluster ej1@xxx.xxx.xxx.xx' !!! Stopping ejabberd...
ej3con  | [os_mon] memory supervisor port (memsup): Erlang has closed

[badlop]

- ERLANG_NODE_ARG=ej1@subdomain.domain.com

That environment variable is read by the ejabberdctl script, and it is passed to the erl virtual machine as the argument -sname (or -name when the value has subdomains with a dot .). As a result, the erlang virtual machine names itself as ej1@subdomain.domain.com.

---

docker exec ej1container ejabberdctl status
Failed RPC connection to the node 'ej1@subdomain.domain.com': nodedown

I get that same problem with a similar compose file:

Details

version: '3.7'

services:

  main:
    image: ghcr.io/badlop/ejabberd:dependabot
    container_name: ejabberd
    hostname: ej1container
    environment:
      - ERLANG_NODE_ARG=ejabberd@subdomain.domain.com
      - ERLANG_COOKIE=dummycookie123

The solution in my case is to add subdomain.domain.com to /etc/hosts inside the container. That way ejabberdctl is able to connect correctly to the running node and get the status.

---

ERLANG_NODE_ARG=ej1@ej1container
ejabberdctl join_cluster ej1@subdomain.domain.com
** System NOT running to use fully qualified hostnames **

Right, you used the erlang short node name ej1container, so you cannot later use a long node name like sub.domains

Either use:

ERLANG_NODE_ARG=ej1@ej1container
ejabberdctl join_cluster ej1@ej1container

If you use this in different machines, make sure the second one knows where to find ej1container (by adding it to /etc/hosts for example)

Or use:

ERLANG_NODE_ARG=ej1@ej1container.domain.com
ejabberdctl join_cluster ej1@ej1container.domain.com

In that case, make sure erlang can know what does ej1container.domain.com point to.

[etranger7]

Thank you for your reply @badlop .
Here is what worked for me to move past the
"Failed RPC connection to the node 'ej1@subdomain.domain.com': nodedown"
message and get a positive STATUS message. In the docker compose file, I used

services:
  ejabberd:
    image: ejabberd/ecs:24.07
    container_name: ejabberd
    hostname: subdomain.domain.com
    environment:
      - CTL_ON_START=status
      - ERLANG_COOKIE=[removed]
      - ERLANG_NODE_ARG=ejabberd@subdomain.domain.com

However, when I try to connect to ejabberd@subdomain.domain.com that's on Server A, from Server B, I get

Error: error
Error: "This node cannot reach that node."

When I

docker exec ejabberd bin/ejabberdctl ping ejabberd@subdomain.domain.com

from Server B, I get pang.

When I ping Server A from Server B, I can reach it with no issues.

When I

docker exec -u root ejabberd ping subdomain.domain.com

from server B to Server A, again Server A is reachable.

I feel like I'm missing something here.
Again, your help is much appreciated.

[etranger7]

Hi @badlop , should I re-submit this issue under the issues of https://github.com/processone/ejabberd/ ?
I'm wondering whether that's being more closely monitored and whether the issues with the containers should also be submitted there.
Thanks.

[badlop]

This is a problem with that container image, so here seems a good place for the issue.

On the other hand, it may be a problem related to docker and erlang clustering, not only ejabberd, and you may search for related questions outside of ejabberd places.