Accessing environment variables from within scripts about s6-overlay

[glerchundi]

with-contenv is the way to go. It was coded with execline in mind (chaining processes) but it can be used with other kind of scripting languages of course!

Try this:

#!/usr/bin/with-contenv sh

# cd into our directory
cd /app

# start our node.js application
exec node server.js;

[skarnet]

Yes, there's a 4096 byte limit for variables loaded via s6-envdir. This is intentional: most legitimate uses of the environment never transmit large quantities of data. You can put the data in a temporary file, put the name of the file in an environment variable, and make your application get its data from the file.

Alternatively, you could recompile skalibs, then s6 after increasing the limit here: [http://git.skarnet.org/cgi-bin/cgit.cgi/skalibs/tree/src/libstddjb/envdir.c#n12] but it will not be standard and you will need to maintain the patch.

[smebberson]

Awesome, that works perfectly :)

Do you think this is worth adding to the documentation, the README? I'd be happy to submit a PR with this....

[smebberson]

Just wanted to add that when I run a script through docker exec everything works fine, the environment variables exist. But when the script is run through s6, they don't.

[glerchundi]

PR are always welcome, and if they are to document, even better!

[smebberson]

@glerchundi, also, am I correct in thinking that in your example, node would also have the same environment variables despite the fact it was exec'd?

Alright, I'll get to work!

[glerchundi]

@glerchundi, also, am I correct in thinking that in your example, node would also have the same environment variables despite the fact it was exec'd?

yeah, i think so: http://ss64.com/bash/exec.html

[jprjr]

@smebberson That should work - exec only clears the environment when you use the -c switch.

[smebberson]

@glerchundi, just to be clear, for documentation purposes.

From reading the code, if I have a script that sets environment variables using setenv or export this won't make it's way into the /var/run/s6/container_environment directory... I could be wrong?

If they don't, that means running a script with #!/usr/bin/with-contenv sh won't pick up the new environment variables... how should one go about doing this kind of thing with s6-overlay?

[glerchundi]

You're correct. In runtime you can make it available if you create a file (naming it with your desired env name) and fill it with your custom value. Something like this: printf "YOURVALUE" > /var/run/s6/container_environment/YOURENV.

That should do the trick.

[apratina]

@glerchundi @jprjr @smebberson @skarnet : using with-contenv bash we are unable to use any environment variable of length greater than 4096 char. Is this a known issue?
I have created a very simple way to repro it. Check here.

[VINAYJAGANNATH]

Can the limit of 4096 bytes made configurable ?
If yes this would give us great flexibility to inject environment variables which have higher than 4096 bytes.
We have a use case for this, Where in Cloud Foundry all the service bindings are injected as part of ENV and we have no control over the injection to the init process.
We tried using S6-Overlay as init process and due to this limit the all the service binding properties are no injected to the application process which is managed by S6-Overlay.

[skarnet]

My previous post suggests two ways of achieving what you want.