aws cli lambda `update-function-configuration` deletes existing environment variables

Question

The documentation on the AWS cil lambda states that

...You provide only the parameters you want to change...

Which I assume means that the rest of the settings would still remain the same. However, say my lambda function has environment variables :

var1=old_val1
var2=old_val2
var3=old_val3

and then when I try doing something like this :

aws lambda update-function-configuration --function-name dummy_fun --environment '{"Variables":{"var1":"new_val1","var2":"new_val2"}}'

with the intention of updating the variables : var1 and var2 with the new values new_val1 and new_val2 respectively, although these 2 variables DO get updated, but the third one, var3, gets deleted !

Am I doing something wrong ? Or is there a way to make sure this doesn't happen?

I can definitely handle it using a workaround wherein I can fetch the current config and then update the env variables locally and then push the entire updated config, all of this through a python code etc. But, is that the only way to do it ? Or can there be a simpler way of doing it?

Answer 1

It seems not easy to partially update the environment variables for a lambda with awscli.

But with the usage of the built-in JSON-based client-side filtering that uses the JMESPath syntax, I found a way to achieve what I needed to do.

NEW_ENVVARS=$(aws lambda get-function-configuration --function-name your-func-name --query "Environment.Variables | merge(@, \`{\"ENV_VAR_TO_UPDATE\":\"value_here\"}\`)")

aws lambda update-function-configuration --function-name your-func-name --environment "{ \"Variables\": $NEW_ENVVARS }"

Of course, you can update more than one environment variable with that trick.