CodeBlanks Logo Icon CodeBlanks
Login Register

Dockerfile

Learn to write a Dockerfile for a Go app.

Dockerfile

A Dockerfile is a text file describing step by step how to build an image. The simplest Go Dockerfile:

FROM golang:1.23
WORKDIR /app
COPY . .
RUN go build -o server .
CMD ["./server"]

FROM sets the base image, WORKDIR the working folder, COPY the files, RUN the build command and CMD the command run when the container starts. docker build -t app . builds the image.

.dockerignore

COPY . . sends everything in the folder. A .dockerignore file leaves out unneeded or secret files, speeds up builds and protects the cache:

.git
*.env
bin/
node_modules/

If you use ENTRYPOINT instead of CMD, arguments given to the container are appended to your program.

Practice Container-ready server

A server running in a container must listen on all interfaces. Write addr(port string) string returning ":" + port. Print addr("8080").

Starter code

main.go
package main

import "fmt"

func main() {
    // buraya yaz
}

Sample solution

main.go
package main

import "fmt"

func addr(port string) string {
    return ":" + port
}

func main() {
    fmt.Println(addr("8080"))
}

Expected output

:8080

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What is the biggest problem of this single-stage image?

  • Go can't compile
  • It can't open a port
  • The whole Go toolchain stays in the image, making it hundreds of MB Correct answer
  • It doesn't run

Explanation: The golang base contains the compiler and libraries (~800 MB); running needs only the binary. Multi-stage builds solve this.

2 Base image

Question 
____ golang:1.23
WORKDIR /app
Answer 
FROM golang:1.23
WORKDIR /app

Explanation: FROM is the first instruction of every Dockerfile and chooses the base image.

3 Instruction and role

Term Meaning
FROM Base image
COPY Copies files
RUN Build-time command
CMD Startup command

All lessons in Advanced

1 Reflection

  1. The reflect package
  2. reflect.Type
  3. reflect.Value
  4. Reflecting struct fields
  5. Dynamic call
  6. Summary - Reflection

2 unsafe

  1. The unsafe package
  2. unsafe.Pointer
  3. Sizeof and Alignof
  4. Offsetof
  5. unsafe and slice
  6. Summary - unsafe

3 cgo

  1. What is cgo?
  2. Calling C code
  3. C data types
  4. Go-C conversion
  5. cgo and memory
  6. Summary - cgo

4 plugin

  1. The plugin package
  2. Building a plugin
  3. Loading a plugin
  4. Plugin symbol
  5. Plugin and error
  6. Summary - plugin

5 database/sql

  1. The database/sql package
  2. sql.Open
  3. Query and Exec
  4. Prepared statement
  5. Transaction
  6. Summary - database/sql

6 Middleware

  1. The middleware concept
  2. HTTP middleware
  3. Middleware chain
  4. Logging middleware
  5. Auth middleware
  6. Summary - Middleware

7 gRPC

  1. What is gRPC?
  2. Protobuf definition
  3. Compiling with protoc
  4. gRPC server
  5. gRPC client
  6. Summary - gRPC

8 Project: Microservice

  1. Service skeleton
  2. Database layer
  3. HTTP API
  4. Docker and deployment

9 Docker

  1. Dockerfile
  2. Multi-stage build
  3. scratch image
  4. docker-compose
  5. Build args and labels
  6. Summary - Docker

10 pprof

  1. What is pprof?
  2. CPU profiling
  3. Memory profiling
  4. go test -cpuprofile
  5. The trace tool
  6. Summary - pprof

11 Observability

  1. log/slog
  2. Metrics
  3. Tracing
  4. OpenTelemetry
  5. Health check
  6. Summary - Observability

12 Advanced final

  1. Challenge 1 - Reflection
  2. Challenge 2 - Microservice
  3. Challenge 3 - Performance
  4. Challenge 4 - Database