[VScode] Docker+Go+air+delveでリモートデバッグ

はじめに

Docker上で動いているGo言語のアプリケーションを、VScodeでリモートデバッグします。
その際に、デバッガツールの delve と、ホットリロードツールの air を使います。

ディレクトリ構成

├── .vscode
│   └── launch.json
├── cmd
│   ├── .air.toml
│   ├── go.mod
│   └── main.go
├── Dockerfile
└── docker-compose.yml

Dockerfile

まず、Dockerで以下の２つをインストールします。

FROM golang:1.17.2

RUN go install github.com/go-delve/delve/cmd/dlv@latest
    
RUN go install github.com/cosmtrek/air@latest

docker-compose.yml

version: '3.7'
services:
  app:
    build: .
    ports:
      - "2345:2345" #delve用のポート
    volumes:
      - ./:/go/src
    working_dir: /go/src/cmd
    command: air -c .air.toml

commandでairを実行しています。
（airの設定ファイル.air.tomlの中で、delve実行も設定している）

.air.toml

air_example.toml
こちらをコピペして使いました。
変更ポイントは、cmdとfull_binだけです。

# Config file for [Air](https://github.com/cosmtrek/air) in TOML format

# Working directory
# . or absolute path, please note that the directories following must be under root.
root = "."
tmp_dir = "tmp"

[build]
# Just plain old shell command. You could use `make` as well.
cmd = "go build -gcflags \"all=-N -l\" -o tmp/main ."
# Binary file yields from `cmd`.
bin = "tmp/main"
# Customize binary.
full_bin = "dlv --listen=:2345 --headless=true --api-version=2 --accept-multiclient exec ./tmp/main"
# Watch these filename extensions.
include_ext = ["go", "tpl", "tmpl", "html"]
# Ignore these filename extensions or directories.
exclude_dir = ["assets", "tmp", "vendor", "frontend/node_modules"]
# Watch these directories if you specified.
include_dir = []
# Exclude files.
exclude_file = []
# Exclude specific regular expressions.
exclude_regex = ["_test.go"]
# Exclude unchanged files.
exclude_unchanged = true
# Follow symlink for directories
follow_symlink = true
# This log file places in your tmp_dir.
log = "air.log"
# It's not necessary to trigger build each time file changes if it's too frequent.
delay = 1000 # ms
# Stop running old binary when build errors occur.
stop_on_error = true
# Send Interrupt signal before killing process (windows does not support this feature)
send_interrupt = false
# Delay after sending Interrupt signal
kill_delay = 500 # ms

[log]
# Show log time
time = false

[color]
# Customize each part's color. If no color found, use the raw app log.
main = "magenta"
watcher = "cyan"
build = "yellow"
runner = "green"

[misc]
# Delete tmp directory on exit
clean_on_exit = true

• cmd = "go build -gcflags \"all=-N -l\" -o tmp/main ."
dlv exec を使うためには、-gcflags=all='-N -l'が必要になります。

go build
-gcflags '[pattern=]arg list'
arguments to pass on each go tool compile invocation.

• full_bin =
  "dlv --listen=:2345 --headless=true --api-version=2 --accept-multiclient exec ./tmp/main"

cf.　dlvコマンドのoption詳細
--api-version int Selects API version when headless. New clients should use v2. Can be reset via RPCServer.SetApiVersion. See Documentation/api/json-rpc/README.md. (default 1)
--accept-multiclient Allows a headless server to accept multiple client connections.

.vscode/launch.json

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Remote",
            "type": "go",
            "request": "attach",
            "mode": "remote",
            "remotePath": "/go/src/cmd",
            "port": 2345,
            "host": "localhost",
            "cwd": "${workspaceRoot}/cmd",
            "env": {},
            "args": [],
        }
    ]
}

• name: お好きな名前
• type: デバッガーの種別
• request: デバッグ時にプログラムを起動するか（launch）、
  既に起動しているプログラムにデバッガーをアタッチするか（attach）
• remotePath: コンテナ内のパス
• port: dlvのポート
• cwd: デバッグ実行を行うディレクトリ
• ${workspaceRoot}: VSコードで開いたディレクトリのパス

詳細：launchjson-attributes