88 lines
2.3 KiB
Markdown
88 lines
2.3 KiB
Markdown
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# Multistage & Layers
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Previously, in [Topic 2, Working with Code](working_with_code.md), we have dockerfile to create isolated DEV environment, but we still have to manually `dotnet new/build/run`
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Target: Use multistage dockerfile to automatically setup DEV & PROD environment, where we only need to modify source code.
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## What is Docker Image Layering?
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dockerfile lay layers on top of another. So often changed layers should be in bottom to save image building time
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### General DEV + PROD multistage dockerfile structure
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```dockerfile
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######## Dev stage #########
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# Start from a base image (Layer 1)
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FROM base-SDK-image-here
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# install dependencies (Layer 2)
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RUN pip install \npm install \go get
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# Copy source code into image (Layer 3)
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COPY source
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# Run assembly to build app based on source code (Layer 4)
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RUN build
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```
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Above is the dockerfile for a development environment. To product ready, we can use multistage. By giving above codes an alias, we can build multi-stage images
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continue dockerfile
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```dockerfile
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####### Runtime stage #########
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# Using a runtime image instead of full SDK (Layer 5)
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FROM another-image
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# Copy compiled app into runtime image to save space (Layer 6)
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COPY output-from-stage-1
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# Start app or entrypoint
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RUN application
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```
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Benefit of this multistage, we can use debug tools in dev stage, but also keep product small in stage 2
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## Modify dockerfile and docker-compose for multistage building
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### Add build target in docker-compose
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Adding build target in `build`, so docker-compose can be directly used to create DEV/PROD image.
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```docker-compose
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build:
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context: ./c#
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target: dev
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```
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### Modify dockerfile
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```dockerfile
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############# DEV IMAGE #################
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# Define a dev stage using `as`
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FROM mcr.microsoft.com/dotnet/core/sdk:2.2-stretch as dev
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# Defining a working directory
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RUN mkdir /app/
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WORKDIR /app/
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# ????
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COPY ./src/work.csproj /app/work.csproj
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RUN dotnet restore
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# Copy the remaining source file
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COPY ./src/ /app/
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RUN mkdir /out/
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RUN dotnet publish --no-restore --output /out/ --configuration Release
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############## PRODUCT IMAGE #############
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FROM mcr.microsoft.com/dotnet/core/sdk:2.2-stretch-slim as prod
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RUN mkdir /app/
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WORKDIR /app/
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# Copy binary into folder
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COPY --from=dev /out/ /app/
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RUN chmod +x /app/
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CMD dotnet work.dll
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```
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