MTU Configuration for Custom Networks

Problem

In Terraform Enterprise versions 202104-1 and later, component containers use the custom Docker networks tfe_services and tfe_terraform_isolation. These networks provide better isolation but do not automatically inherit the Maximum Transmission Unit (MTU) setting from the Docker daemon's daemon.json configuration file.

This can cause intermittent network connectivity issues during Terraform runs if your environment requires a custom MTU value. This guide provides the procedure to recreate these networks with the correct MTU setting.

Prerequisites

• Shell access to the Terraform Enterprise instance.
• Sudo or root privileges.

Procedure

Follow these steps to reconfigure the Docker networks with a custom MTU value. This example uses an MTU of 1460.

1. Stop the Terraform Enterprise application.

   $ replicatedctl app stop

2. Verify that the application has stopped. The status should show stopped.

   $ replicatedctl app status

3. Remove the existing tfe_terraform_isolation Docker network.

   # docker network rm tfe_terraform_isolation

4. Remove the existing tfe_services Docker network.

   # docker network rm tfe_services

5. Recreate the tfe_terraform_isolation network with your custom MTU setting.

   # docker network create tfe_terraform_isolation \
     --subnet=172.20.0.0/16 \
     --gateway 172.20.0.1 \
     -o com.docker.network.driver.mtu=1460

6. Recreate the tfe_services network with your custom MTU setting.

   # docker network create tfe_services \
     --subnet=172.19.0.0/16 \
     --gateway 172.19.0.1 \
     -o com.docker.network.driver.mtu=1460

7. Verify the new settings for the tfe_terraform_isolation network. Check the Options section in the output for the com.docker.network.driver.mtu key.

   # docker network inspect tfe_terraform_isolation

   Example Output:

   [
       {
           ##...
           "Options": {
               "com.docker.network.driver.mtu": "1460"
           },
           ##...
       }
   ]

8. Verify the new settings for the tfe_services network.

   # docker network inspect tfe_services

9. Start the Terraform Enterprise application.

   $ replicatedctl app start

Additional Information

For more details on Docker networking, we suggest reviewing the official Docker documentation.