Setting environment variables in Dokku


Where we take a look at setting environment variables in Dokku.

Dokku is an amazing, minimalistic system for getting your single, amateur programmer deployment needs out of the way effectively. I already talked extensively about it in Dokku - Your Tiny PaaS.

Setting environment variables can bite you

One thing that hit me recently is how you can set environment variables (either globally or for a specific application). The sub command is config, and in particular config:set, like this:

ssh $DOKKU config:set KEY='wow, a value here'

Yes, I’m using the low-level interface, i.e. the plain SSH connection.

It so happens that this interface is not exactly robust. By design reasons which are unknown to me, the command above saves the key/value pair in a file that can be sourced easily, but decides to adopt double quotes for saving the thing, like this:

KEY="wow, a value here"

Moreover, it seems to fail spectacularly with newlines.

In-house solution

If you want to be on the safest side, you can encode the whole thing in a single, long, base64-encoded string and then set it in the environment:

ssh $DOKKU config:set myapp \
    KEY="$(printf %s "$VALUE" | base64 -w 0)"

Note that we are passing -w 0 to base64, otherwise it will eventually insert a newline and break the whole thing again.

Then, in your code, you can decode it back:

use MIME::Base64 'decode_base64';
# ...
my $text = decode_base64($ENV{KEY});

This is it, totally under your control.

Assisted solution

Dokku actually assists you with the server-side half of the solution in the previous section. If you pass parameter --encoded to config:set, you’te telling Dokku that the value is base64-encoded and it should treat it as such, decoding before saving the environment variable:

ssh $DOKKU config:set --encoded myapp \
    KEY="$(printf %s "$VALUE" | base64 -w 0)"

Now you have to trust that the escaping in saving the variable is done properly, but with this you can just do this in your code:

my $text = $ENV{KEY};

i.e. the same as single-line simple-text stuff. Neat!

The bottom line

If you’re lazy and want to just learn one thing, it’s that you should ALWAYS set variables like this:

VALUE='...' # whatever, with newlines or not
ssh $DOKKU config:set --encoded myapp \
    KEY="$(printf %s "$VALUE" | base64 -w 0)"

This will work independently of how complex the $VALUE is and never fail you.

Well… never say never, but you get the idea.

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