AppSettings Merger

The typical ASP.NET Core project supports stacking appSetttings.json files so that more specific files, e.g. appSettings.{Environment}.json files, overwrite the more generic appSettings.json file.

The purpose is to have most settings placed in appSettings.json and place in the environment overwrite files only those settings which are different from the base-line.

In my experience, long-running projects tend to duplicate settings between the appSettings.Development.json and appSettings.Production.json or appSettings.Staging.json, and these settings no longer get migrated back into the appSettings.json.
This, in turn, makes configuration management a bit more difficult over time, as well as other operations like PR reviews, deployments, etc.

This project solves this case where settings are spread inefficiently over several files and attempts to re-create a base appSettings.json file and only keep those values that are different in other files.

Operation

The parameters of the project are a list of files to inspect and attempt to merge.
The "algorithm" is fairly naive so the appSettings.json file should be specified first.

For example, assuming:

• appSettings.json contains:

{
  "Publish": {
    "TopicName": "books-read"
  }
}

• appSettings.Development.json contains:

{
"Publish": {
    "TopicName": "books-read-dev",
    "MaxMessages": 5
},
"ConnectionStrings": {
    "Default": "Server=localhost;Database=books;Trusted_Connection=True"
}
}

• appSettings.Production.json contains:

{
  "Publish": {
    "TopicName": "books-read",
    "MaxMessages": 10
  },
  "ConnectionStrings": {
    "Default": "Server=my-prod-serve;Database=books;Trusted_Connection=True"
  }
}

Calling AppSettingsMerger with appSettings.json appSettings.Development.json appSettings.Production.json will result in:

// appSettings.json
{
  "Publish": {
    "TopicName": "books-read",
    "MaxMessages": 5
  },
  "ConnectionStrings": {
    "Default": "Server=localhost;Database=books;Trusted_Connection=True"
  }
}

// appSettings.Development.json
{
  "Publish": {
    "TopicName": "books-read-dev"
  }
}

// appSettings.Production.json
{
  "Publish": {
    "MaxMessages": 10
  },
  "ConnectionStrings": {
    "Default": "Server=my-prod-serve;Database=books;Trusted_Connection=True"
  }
}

Each environment file now contains the values that differ from appSettings.json making, in this author's humble opinion, easier to reason about settings for each environment.

How to run

There are no releases at this time. Clone the project then use dotnet run --project to run it.

For example, if you cloned it in ~/Projects/AppSettingsMerger and you would like to merge the files in ~/Projects/MyCompany/MyWebApp/MyWebApp.API, you would navigate to ~/Projects/MyCompany/MyWebApp/MyWebApp.API and then invoke:
dotnet run --project=~/Projects/AppSettingsMerger/AppSettingsMerger.csproj appSettings.json appSettings.Development.json appSettings.Production.json

There is a convenient --dry-run flag you can specify to show the output, without altering the files, but typically I found that leaving it out, having AppSettingsMerger change the files, then using even the barest VCS commands to diff the changes produced better results.
After all, undoing is just a git checkout -f away.