Category: Google Cloud

GCE – Open Up Port 8025 in VPC for MailHog

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If you want to use MailHog ( https://github.com/mailhog/MailHog ) on your Google Compute Engines (GCE) you probably have to create a new VPC firewall rule in your project. In this post, I will skip the installation and configuration part of MailHog with Supervisord, because there are so many different ways to set up MailHog.

By default, the MailHog interface is running on port 8025.

Mailhog GUI interface

Once the MailHog process is up and running, you probably won’t be able to access your server on port 8025. This is because those ports are not defined in VPC. In order to get access from outside, you must create a new firewall rule in your GCE project. This can be done in the Google console or simply via the command-line. Here is how I created a new rule ” custom-allow-mailhog ” for port 8025.

Once the rule has been created, you should be able to open the interface of MailHog.

GCE – SSH Directly Into Your Docker Container

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In this article, I am going to change the SSH port from 22 to 52241 and create a new firewall rule in VPC. Please do your own research and make sure you understand the impact, especially on a production environment.

When you deploy a new docker container on GCE, you can SSH into the host machine ( VM ). This is simply because the IP address is pointing to the host machine. But what about the docker container that runs on it? In this case, you must use docker exec or the gcloud command-line tool in order to get access to the container, which can be pretty time consuming over time.

I am working on a project where I need direct access to my alpine docker container on port 22 or any other port. As you can see in the below output, no ports are exposed for my container.

This is mainly because the docker container shares the network with the host. Source

Containerized VMs launch containers with the network set to host mode. A container shares the host network stack, and all interfaces from the host are available to the container.

This is very convenient because it allows you to access your docker container from pretty much any port. However, only a few ports are actually open and configured in the VPC Network > Firewall settings for security reasons. For the SSH connection I decided to open a custom port 52241. You can do this in your GCP Console under VPC Network > Firewall or with the following gcloud command-line tool.

Once completed, here is how the new firewall rule looks like in the console. If you scroll down, you will also see all affected instances.

GCP Custom Firewall

Before you can SSH into your container on port 52241 you must change the port in the sshd configuration /etc/ssh/sshd_config within your container or container image. Not on the VM.

You may have to restart your ssh service before you can use the new port. Once this is done, you can SSH into your docker container.