How to ping a private host within a private network?

July 20, 2019 245 views
Nginx DigitalOcean Cloud Firewalls Ubuntu 18.04

I’ve created two VPS droplets running ubuntu 18.04 on each. Droplet #1 will be a load balancer powered by nginx. Droplet #2 will be an app server layer running node JS on port 3000.

I am trying to reverse proxy requests to the node server but it seems I am unable to communicate with the two instances.

In order to debug this, I am trying to simply determine how to get one droplet to communicate to another droplet using the private IP.

Currently, when I ping or telnet to the private IP of droplet #2, I get 100% loss of packets for ping and telnet does not respond either.

Can you please help me to understand if I am missing a firewall rule or some other configuration setting to get the two to communicate? I would have thought they could communicate over the private network.

Thanks,
Gregg

1 Answer

Hello Gregg,

As a quick bit of caution, private network settings will only work across Droplets in the same Datacenter on the same account. With that in mind, let’s dig in a bit more!

Could you please confirm private networking is enabled and configured in both the Droplets?

You can verify the configuration from the below link::

https://www.digitalocean.com/docs/networking/private-networking/how-to/enable/#verify-the-configuration

Once you confirm the above two steps are done in the Droplet. Are you able to ping the Droplets now? If not then please open a Support ticket with the output the below commands::

For network interfaces currently in use:: ip addr
To ensure that routing to your gateway is working properly:: ip route

If you are able to ping now then please cross-check the below points:

  1. Are the services ( application, LoadBalancer) bound to eth1 interfaces (or 0.0.0.0, not 127.0.0.1 )?
  2. Does the firewall allow traffic from LB <-> application (inbound 3000).
  3. Does the firewall allow traffic to LB (inbound 80) for public internet?

If you are still facing the issue, it may be best to reach out to our Support team to get some specific details regarding the private networking. Let me know if you have any other questions.

  • Purnima,
    Thank you for your detailed response. I will give this a try.

Have another answer? Share your knowledge.