InitContainer with Entity Framework Core and Oracle

When you are using Entity Framework Core and Oracle, you may want to create an InitContainer for Kubernetes to handle your Database migrations.

Multistage Dockerfile

ARG VERSION=0.1.0
FROM mcr.microsoft.com/dotnet/aspnet:7.0 AS base
WORKDIR /app
EXPOSE 8080
ENV ASPNETCORE_URLS=http://+:8080


FROM mcr.microsoft.com/dotnet/sdk:7.0 AS build
ARG VERSION
ARG configuration=Release
WORKDIR /src
COPY . .
WORKDIR "/src/SOMEPROJECT"
RUN dotnet restore "SOMEPROJECT.csproj"
RUN dotnet build "SOMEPROJECT.csproj" -c $configuration -o /app/build -p:Version=${VERSION}

FROM build as migrationbuilder
ENV PATH $PATH:/root/.dotnet/tools
RUN dotnet tool install --global dotnet-ef
RUN mkdir /migrations
RUN dotnet ef migrations bundle --self-contained -r linux-x64 -o /migrations/migration
RUN cp ./initentrypoint.sh /migrations/initentrypoint.sh

FROM mcr.microsoft.com/dotnet/runtime:7.0 as initcontainer
ENV CONNECTIONSTRING="User Id=ORACLEUSER;Password=ORACLEPASSWORD;Data Source=db:1521/FREEPDB1;"
COPY --from=migrationbuilder /migrations /migrations
COPY --from=migrationbuilder /src/src/AksPoc/appsettings.json /migrations/appsettings.json
RUN chmod 755 /migrations/migration
RUN chmod 755 /migrations/initentrypoint.sh
WORKDIR /migrations
ENTRYPOINT [ "./initentrypoint.sh" ]

FROM build AS publish
ARG configuration=Release
RUN dotnet publish "SOMEPROJECT.csproj" -c $configuration -o /app/publish /p:UseAppHost=false

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "SOMEPROJECT.dll"]

Initscript

#!/bin/bash
./migration --connection "$CONNECTIONSTRING"

How to build the InitContainer

docker build --target initcontainer -t initcontainer:latest .

How to build the application container

docker build -t appcontainer:latest .

How does it work

To build an InitContainer you just need to add 2 new Stages in your DockerFile.

Stage 1 — Migrationbuilder:

This stage is using the .net sdk and installing the dotnet-ef tools to build a migration bundle.

Stage 2 — Initcontainer

This stage holds the code to run your migrations in kubernetes. It can be build by setting the option target in the docker build:

--target initcontainer

When you now run your initcontainer you simply need to set the environment variable “CONNECTIONSTRING” to a valid oracle .net connectionstring.

Good to know:

• Migrationbundles need a valid appsettings.json next to the migration bundle
• You should mount a tnsnames.ora into the container
• You should set the environment variable TNS_ADMIN to point to the folder containing tnsnames.ora
• The initscript is launching the migration with the connectionstring from your environment variable “CONNECTIONSTRING”