August 31, 2021

August 31, 2021
tools direnv

Changing environments per directory

While discussing tmux as a tool with a colleague the question came up: could we automagically switch the gcloud configuration when switching between tmux sessions?

For example, I have a tmux session for a project called TrainTrack. When I’m working on that project I’d like to have my gcloud config point to a specific GCP project.

And when I switch tmux sessions to work on my dispatcher project, I similarly want to have the gcloud configuration switch—automatically—to the relevant GCP project.

You can achieve this manually by setting an environment variable called CLOUDSDK_ACTIVE_CONFIG_NAME, so what I need is a way to change that ENV variable automatically when I switch working directories.

`direnv`

The Google documentation points to direnv as a viable solution.

It uses the presence of a .envrc file in a directory to trigger loading and unloading and resetting ENV values.

Installation

Piece of cake on Mac: brew install direnv then integrate into your shell.

Setup

I’m using tmux so I created a session where I have two project directories open, one per pane. My goal is to be able to simple switch between panes in the same tmux session and have the gcloud configuration change automatically.

Pane #1 - I’m in a directory called traintrack:

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echo "CLOUDSDK_ACTIVE_CONFIG_NAME=ttrack" > .envrc

At this point direnv let me know that it needs permission to automatically update environment variables:

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direnv allow

Pane #2 - directory for my ‘dispatcher’ project that needs a different gcloud config. Note the different value for the CLOUDSDK_ACTIVE_CONFIG_NAME variable that the gcloud command is watching for:

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echo "CLOUDSDK_ACTIVE_CONFIG_NAME=dispatcher" > .envrc
direnv allow

Proving it out

With tmux open and two panes side-by-side I start in pane #1:

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$ gcloud config list
[core]
account = dylan.thomas@woolpert.com
disable_usage_reporting = True
project = fleetrouting-app-dev

Your active configuration is: [dispatcher]

Bingo! I have the correct configuration [dispatcher] for this project directory.

Then switch to Pane #2 and run the same command:

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gcloud config list
[core]
account = dylan.thomas@woolpert.com
disable_usage_reporting = True
project = demos-landing-site-quenthal

Your active configuration is: [ttrack]

And yes! Without doing anything at all I have the correct and expected gcloud configuration with the right project, etc.

I can see this being really useful for configuring 12 Factor apps.