在谷歌云平台（GCP）上连接 Erlang/Elixir VM 节点的问题，相同的 VPC - 不同的区域，MNESIA 无法复制

Question

I am trying to connect two Erlang VMs (running on Centos 8, Erlang/OTP 23), one located on GCP us-east1-b and other GCP europe-west6, both inside same VPC, running on separate subnets, us-east 10.33.0.0/16 eur-west on 10.88.0.0/16. GCP routes and firewalls should be set to allow traffic across those subnets and throughout the VPC. Ping works from VM to VM (see below). Telnet works to erlang epmd port 4369. ISSUE - when connecting machine to machine using erlang ping utility net_adm:ping()/1 - returns a "pang", meaning does not connect.

Any suggestions or thoughts on what might be the issues, much appreciated !!!

Here is additional research and facts RE the setups.

NOTE - the GCP firewall rules, note the GCP network "block" ing result on the test connection, and note the TELNET responses for ports 35539 and 42257 do not connect (which maybe explains why the VM's return a "pang" or can't connect)

[g@app-server1-east ~]$ erl -name ack1@10.33.0.2 -setcookie whale
Erlang/OTP 23 [erts-11.1.3] [source] [64-bit] [smp:2:2] [ds:2:2:10] [asy
nc-threads:1] [hipe]
Eshell V11.1.3  (abort with ^G)
(ack1@10.33.0.2)1> net_adm:ping('ack2@10.88.0.2').
pang
(ack1@10.33.0.2)2> 

[g@app-server1-east ~]$ ping 10.88.0.2
PING 10.88.0.2 (10.88.0.2) 56(84) bytes of data.
64 bytes from 10.88.0.2: icmp_seq=1 ttl=64 time=105 ms
64 bytes from 10.88.0.2: icmp_seq=2 ttl=64 time=103 ms
64 bytes from 10.88.0.2: icmp_seq=3 ttl=64 time=104 ms
64 bytes from 10.88.0.2: icmp_seq=4 ttl=64 time=103 ms
64 bytes from 10.88.0.2: icmp_seq=5 ttl=64 time=103 ms
^C
--- 10.88.0.2 ping statistics ---
6 packets transmitted, 5 received, 16.6667% packet loss, time 12ms
rtt min/avg/max/mdev = 103.290/103.749/105.243/0.754 ms
[g@app-server1-east ~]$ epmd -names
epmd: up and running on port 4369 with data:
name ack1 at port 35539
[gbaird@app-server1-east ~]$ telnet 10.88.0.2 4369
Trying 10.88.0.2...
Connected to 10.88.0.2.
Escape character is '^]'.
exit
Connection closed by foreign host.
[g@app-server1-east ~]$ telnet 10.88.0.2 42257
Trying 10.88.0.2...
telnet: connect to address 10.88.0.2: Connection timed out here

---

[g@app-server2-eur ~]$ erl -name ack2@10.88.0.2 -setcookie whale
Erlang/OTP 23 [erts-11.1.3] [source] [64-bit] [smp:2:2] [ds:2:2:10] [asyn
c-threads:1] [hipe]
Eshell V11.1.3  (abort with ^G)
(ack2@10.88.0.2)1> node 
(ack2@10.88.0.2)1> .
node
(ack2@10.88.0.2)2> 
  

g@app-server2-eur ~]$ ping 10.33.0.2
PING 10.33.0.2 (10.33.0.2) 56(84) bytes of data.
64 bytes from 10.33.0.2: icmp_seq=1 ttl=64 time=105 ms
64 bytes from 10.33.0.2: icmp_seq=2 ttl=64 time=103 ms
64 bytes from 10.33.0.2: icmp_seq=3 ttl=64 time=103 ms
64 bytes from 10.33.0.2: icmp_seq=4 ttl=64 time=103 ms
^C
--- 10.33.0.2 ping statistics ---
5 packets transmitted, 4 received, 20% packet loss, time 10ms
rtt min/avg/max/mdev = 103.194/103.601/104.685/0.666 ms
[g@app-server2-eur ~]$ epmd -names
epmd: up and running on port 4369 with data:
name ack2 at port 42257
[gbaird@app-server2-eur ~]$ telnet 10.33.0.2 4369
Trying 10.33.0.2...
Connected to 10.33.0.2.
Escape character is '^]'.
exit
Connection closed by foreign host.
[g@app-server2-eur ~]$ telnet 10.33.0.2 35539
Trying 10.33.0.2...
telnet: connect to address 10.33.0.2: Connection timed out
[gbaird@app-server2-eur ~]$ 

Answer 1

Erlang's EPMD (Erlang Port Mapper Daemon) is the one listening in port 4369, but the node listens in a random port.

When setting up a cluster, the node registers it's port in the local host's EPMD and contacts the remote host's EPMD to query the actual port for the remote node, then the traffic goes directly to that port. EPMD is not a relay.

You can control the range of ports for the nodes to listen through kernel configuration , particularly with inet_dist_listen_min and inet_dist_listen_max , allowing them in the FW