Unable to change environment variable PHX_HOST for deployment

Phoenix
#1

Background

I’ve updated my fly.toml env section for the PHX_HOST entry and it does not update. Instead the env variable remains the internal app host name of "PHX_HOST" => "b4b-guide.fly.dev",.

I’ve removed the variable, changed it and added other environment variables and ended up having to use a separate variable name to get past the problem.

Facts

  • Fly client version: 0.0.323 on macOS Big Sur installed with brew
  • I’ve updated my fly.toml env section to have a different value than b4b-guide.fly.dev.
  • I’ve added other variables to the env file and they were visible
  • To check the env of the deployment I run the following:
fly ssh console
app/bin/app remote
iex> System.get_env()

fly.toml

# redacted...
[env]
  PORT = "8080"
  # For some reason fly is not updating the PHX_HOST variable even if I remove it
  PHX_HOST = "www.myhost.com"
  PHOENIX_HOST = "www.myhost.com"
# redacted ...

To attempt to sync the above fly.toml changes to the PHX_HOST I run fly deploy to no avail.

Problem

No matter the value that is set for PHX_HOST in the fly.toml it remains the original value that was seeded for the application by the flyctl cli.

#2

Strange. That’s one for Fly to investigate however what you could do in the meantime could be to remove that from your fly.toml and instead use a secret to store e.g PHX_HOST. Using fly secrets: Secrets and Fly Apps.

Since secrets are also provided to the app as environment variables at runtime. But they can be set and unset using the CLI, unlike the [env] block in the fly.toml. And they are versioned so can be overwritten.

It is a bit of a hack since of course your hostname does not actually need to be stored as a secret. But it works, so if you need this sorting asap, give that a try.

#3

Strange. That’s one for Fly to investigate however what you could do in the meantime could be to remove that from your fly.toml and instead use a secret to store e.g PHX_HOST . Using fly secrets : Secrets and Fly Apps.

Funny enough I set the secret, then unset it and now the change has picked up from the env. Seems like a small bug in fly more than anything else. This may work for others who run into the problem.

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