docker

During the process of moving a Scala-based API to .NET Core, we encountered an interesting localization issue when running our code in a docker container based on an alpine image. The code itself was doing a currency formatting based on some culture. It looked more or less as below

[Route("api/[controller]")]
[ApiController]
public class PriceController : ControllerBase
{
    [HttpGet]
    public ActionResult<object> Get(string cultureCode = "de-DE")
    {
        var cultureInfo = CultureInfo.CreateSpecificCulture(cultureCode);
        var price = 10m;
        
        return new
        {
            price,
            formattedPrice = price.ToString("C", cultureInfo),
            currencySymbol = cultureInfo.NumberFormat.CurrencySymbol
        };
    }
}

[Route("api/[controller]")]

[ApiController]

public class PriceController : ControllerBase

{

[HttpGet]

public ActionResult<object> Get(string cultureCode = "de-DE")

{

var cultureInfo = CultureInfo.CreateSpecificCulture(cultureCode);

var price = 10m;

return new

{

price,

formattedPrice = price.ToString("C", cultureInfo),

currencySymbol = cultureInfo.NumberFormat.CurrencySymbol

};

}

We also had some integration tests for that piece of logic

public class PriceTests : IClassFixture<WebApplicationFactory<Startup>>
{
    private readonly WebApplicationFactory<Startup> _factory;

    public PriceTests(WebApplicationFactory<Startup> factory)
    {
        _factory = factory;
    }
        
    [Fact]
    public async Task GetPrice_ReturnsCorrectCurrency()
    {
        var httpClient = _factory.CreateClient();
        var httpResponseMessage = await httpClient.GetAsync("api/Price");
            
        httpResponseMessage.EnsureSuccessStatusCode();
        var content = await httpResponseMessage.Content.ReadAsStringAsync();
        var jObject = JObject.Parse(content);

        jObject["currencySymbol"].ToObject<string>().Should().Be("€");
    }
}

public class PriceTests : IClassFixture<WebApplicationFactory<Startup>>

{

private readonly WebApplicationFactory<Startup> _factory;

public PriceTests(WebApplicationFactory<Startup> factory)

{

_factory = factory;

}

[Fact]

public async Task GetPrice_ReturnsCorrectCurrency()

{

var httpClient = _factory.CreateClient();

var httpResponseMessage = await httpClient.GetAsync("api/Price");

httpResponseMessage.EnsureSuccessStatusCode();

var content = await httpResponseMessage.Content.ReadAsStringAsync();

var jObject = JObject.Parse(content);

jObject["currencySymbol"].ToObject<string>().Should().Be("€");

}

The tests were run during a CI build in a container with an image defined as below

# Builder image
FROM mcr.microsoft.com/dotnet/core/sdk:2.1.700-alpine AS builder
WORKDIR /sln

COPY ./*.sln ./

# Copy the main source project files
COPY src/*/*.csproj ./
RUN for file in $(ls *.csproj); do mkdir -p src/${file%.*}/ && mv $file src/${file%.*}/; done

# Copy the test project files
COPY test/*/*.csproj ./
RUN for file in $(ls *.csproj); do mkdir -p test/${file%.*}/ && mv $file test/${file%.*}/; done

RUN dotnet restore

# Copy across the rest of the source files
COPY ./test ./test
COPY ./src ./src

RUN dotnet build -c Release

RUN dotnet test "./test/AlpineMissingCurrencySymbol.Tests/AlpineMissingCurrencySymbol.Tests.csproj" \
    -c Release --no-build --no-restore

RUN dotnet publish "./src/AlpineMissingCurrencySymbol/AlpineMissingCurrencySymbol.csproj" \
    -c Release -o "../../dist" --no-restore

# App image
FROM mcr.microsoft.com/dotnet/core/aspnet:2.1.11-alpine
WORKDIR /app
ENTRYPOINT ["dotnet", "AlpineMissingCurrencySymbol.dll"]
COPY --from=builder /sln/dist .

# Builder image

FROM mcr.microsoft.com/dotnet/core/sdk:2.1.700-alpine AS builder

WORKDIR /sln

COPY ./*.sln ./

# Copy the main source project files

COPY src/*/*.csproj ./

RUN for file in $(ls *.csproj); do mkdir -p src/${file%.*}/ && mv $file src/${file%.*}/; done

# Copy the test project files

COPY test/*/*.csproj ./

RUN for file in $(ls *.csproj); do mkdir -p test/${file%.*}/ && mv $file test/${file%.*}/; done

RUN dotnet restore

# Copy across the rest of the source files

COPY ./test ./test

COPY ./src ./src

RUN dotnet build -c Release

RUN dotnet test "./test/AlpineMissingCurrencySymbol.Tests/AlpineMissingCurrencySymbol.Tests.csproj" \

-c Release --no-build --no-restore

RUN dotnet publish "./src/AlpineMissingCurrencySymbol/AlpineMissingCurrencySymbol.csproj" \

-c Release -o "../../dist" --no-restore

# App image

FROM mcr.microsoft.com/dotnet/core/aspnet:2.1.11-alpine

WORKDIR /app

ENTRYPOINT ["dotnet", "AlpineMissingCurrencySymbol.dll"]

COPY --from=builder /sln/dist .

At this point, we were sure that everything works fine, as the tests were green and everything was also working correctly on our local machines. However, after deployment to a testing environment, we started getting invalid currency symbols

curl localhost:8080/api/price 
{ 
  "price": 10, 
  "formattedPrice": "¤10.00", 
  "currencySymbol": "¤" 
}

curl localhost:8080/api/price

{

"price": 10,

"formattedPrice": "¤10.00",

"currencySymbol": "¤"

}

As you can see the response contains ¤ (invariant currency symbol) instead of expected €. It took us some time to figure this out but finally, it turned out that aspnet:2.1.11-alpine image(the one we used for running the application) contrary to the SDK image(used for building and running tests) is missing icu-libs package. In default conditions, the application should throw the following exception during the startup

FailFast:
Couldn't find a valid ICU package installed on the system. Set the configuration flag System.Globalization.Invariant to true if you want to run with no globalization support.

   at System.Environment.FailFast(System.String)
   at System.Globalization.GlobalizationMode.GetGlobalizationInvariantMode()
   at System.Globalization.GlobalizationMode..cctor()
   at System.Globalization.CultureData.CreateCultureWithInvariantData()
   at System.Globalization.CultureData.get_Invariant()
   at System.Globalization.CultureInfo..cctor()
   at System.StringComparer..cctor()
   at System.AppDomain.InitializeCompatibilityFlags()
   at System.AppDomain.Setup(System.Object)

FailFast:

Couldn't find a valid ICU package installed on the system. Set the configuration flag System.Globalization.Invariant to true if you want to run with no globalization support.

at System.Environment.FailFast(System.String)

at System.Globalization.GlobalizationMode.GetGlobalizationInvariantMode()

at System.Globalization.GlobalizationMode..cctor()

at System.Globalization.CultureData.CreateCultureWithInvariantData()

at System.Globalization.CultureData.get_Invariant()

at System.Globalization.CultureInfo..cctor()

at System.StringComparer..cctor()

at System.AppDomain.InitializeCompatibilityFlags()

at System.AppDomain.Setup(System.Object)

However, aspnet:2.1.11-alpine image has the DOTNET_SYSTEM_GLOBALIZATION_INVARIANT flag set to true by default, so the missing package was not validated during a startup. After all, in order to fix the issue, we had to install the icu-libs package and also set the DOTNET_SYSTEM_GLOBALIZATION_INVARIANT back to false. This was done by these two lines in Dockerfile

ENV DOTNET_SYSTEM_GLOBALIZATION_INVARIANT=false 
RUN apk add --no-cache icu-libs

1 2	ENV DOTNET_SYSTEM_GLOBALIZATION_INVARIANT=false RUN apk add --no-cache icu-libs

Once the lines were added the application started working as expected

curl localhost:8080/api/price 
{ 
  "price": 10, 
  "formattedPrice": "10,00 €", 
  "currencySymbol": "€" 
}

curl localhost:8080/api/price

{

"price": 10,

"formattedPrice": "10,00 €",

"currencySymbol": "€"

}

Source code for this post can be found here

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.NET Core – missing currency symbol in docker alpine image