Override Go app configuration with Environment variable

[Lomanu4]

How to make containerized applications more flexible ?


For at least 10+ years, we develop applications to work in containers. I won't be considering advantages and disadvantages of this approach but want to focus on the application flexibility. Almost every dependency, i.e. storage containers like Postgres, MySql, Redis a so on, allows us to override most of the configuration properties via environment variables. Docker containers stimulate us to use environment variables in our containers. But unlike of well-known services programmers develop custom applications on their own approach. I prefer to configure applications using JSON configuration files. But what should I do if in configuration files 100 and more properties, I can't use Environment variable for each property. Instead of this I decided to use JSON config file as a template with working default values and override properties at application start if appropriate environment variables were set.

How to implement such approach in Go application


Nowadays, we don't use a single Docker image; we prefer to have some orchestration, even something simple like docker-compose. In docker-compose we usually create .env-files. As it was mentioned before, environment variables are working well with well-known images like Postgres or MySQL. Consider we are having the following application config (JSON) that is using as an absolutely working template with the default values.


{
"server": {
"address": "0.0.0.0",
"port": 8182
},
"logging": {
"level": "info",
"http_log": false,
"http_console_out": false
}
}

We should be able to override any of this value; consider that we should increase log level to debug and enable HTTP logging. For doing this easy, we just have to create technical env variables that have a special name pattern:

1. starts with a double underscore __
2. contains full property path, i.e. for log level __logging.level .

Using

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you could do it absolutely easy, all what you have to do:

1. Read JSON object from file using go_config_extender.LoadJSONConfigWithEnvOverride function (you could see full example in a
   
   

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   )
2. Set env file like this:

# all previous variables
__logging.level="debug"
__logging.http_log=true

That's all, and please give us a STAR on GitHub

Conclusion


This approach and package could be used not only for containerized applications but for apps running natively too. This package is successfully working on our

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.

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