Initial Commit

.github/workflows/build.yml

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+name: Build Docker Image
+
+on:
+  push:
+    branches-ignore:
+      - '**'
+    tags:
+      - 'v*'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Generate docker image metadata
+        uses: docker/metadata-action@v5
+        id: metadata
+        with:
+          images: "ghcr.io/${{ github.actor }}/dns-mx-watchdog"
+          tags: |
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: ${{ steps.metadata.outputs.tags }}
+          labels: ${{ steps.metadata.outputs.labels }}

.gitignore

@@ -0,0 +1,144 @@
+# Created by https://www.toptal.com/developers/gitignore/api/go,goland,dotenv
+# Edit at https://www.toptal.com/developers/gitignore?templates=go,goland,dotenv
+
+### dotenv ###
+.env
+
+### Go ###
+# If you prefer the allow list template instead of the deny list, see community template:
+# https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore
+#
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Dependency directories (remove the comment below to include it)
+# vendor/
+
+# Go workspace file
+go.work
+
+### GoLand ###
+# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio, WebStorm and Rider
+# Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839
+
+# User-specific stuff
+.idea/**
+.idea/**/workspace.xml
+.idea/**/tasks.xml
+.idea/**/usage.statistics.xml
+.idea/**/dictionaries
+.idea/**/shelf
+
+# AWS User-specific
+.idea/**/aws.xml
+
+# Generated files
+.idea/**/contentModel.xml
+
+# Sensitive or high-churn files
+.idea/**/dataSources/
+.idea/**/dataSources.ids
+.idea/**/dataSources.local.xml
+.idea/**/sqlDataSources.xml
+.idea/**/dynamic.xml
+.idea/**/uiDesigner.xml
+.idea/**/dbnavigator.xml
+
+# Gradle
+.idea/**/gradle.xml
+.idea/**/libraries
+
+# Gradle and Maven with auto-import
+# When using Gradle or Maven with auto-import, you should exclude module files,
+# since they will be recreated, and may cause churn.  Uncomment if using
+# auto-import.
+# .idea/artifacts
+# .idea/compiler.xml
+# .idea/jarRepositories.xml
+# .idea/modules.xml
+# .idea/*.iml
+# .idea/modules
+# *.iml
+# *.ipr
+
+# CMake
+cmake-build-*/
+
+# Mongo Explorer plugin
+.idea/**/mongoSettings.xml
+
+# File-based project format
+*.iws
+
+# IntelliJ
+out/
+
+# mpeltonen/sbt-idea plugin
+.idea_modules/
+
+# JIRA plugin
+atlassian-ide-plugin.xml
+
+# Cursive Clojure plugin
+.idea/replstate.xml
+
+# SonarLint plugin
+.idea/sonarlint/
+
+# Crashlytics plugin (for Android Studio and IntelliJ)
+com_crashlytics_export_strings.xml
+crashlytics.properties
+crashlytics-build.properties
+fabric.properties
+
+# Editor-based Rest Client
+.idea/httpRequests
+
+# Android studio 3.1+ serialized cache file
+.idea/caches/build_file_checksums.ser
+
+### GoLand Patch ###
+# Comment Reason: https://github.com/joeblau/gitignore.io/issues/186#issuecomment-215987721
+
+# *.iml
+# modules.xml
+# .idea/misc.xml
+# *.ipr
+
+# Sonarlint plugin
+# https://plugins.jetbrains.com/plugin/7973-sonarlint
+.idea/**/sonarlint/
+
+# SonarQube Plugin
+# https://plugins.jetbrains.com/plugin/7238-sonarqube-community-plugin
+.idea/**/sonarIssues.xml
+
+# Markdown Navigator plugin
+# https://plugins.jetbrains.com/plugin/7896-markdown-navigator-enhanced
+.idea/**/markdown-navigator.xml
+.idea/**/markdown-navigator-enh.xml
+.idea/**/markdown-navigator/
+
+# Cache file creation bug
+# See https://youtrack.jetbrains.com/issue/JBR-2257
+.idea/$CACHE_FILE$
+
+# CodeStream plugin
+# https://plugins.jetbrains.com/plugin/12206-codestream
+.idea/codestream.xml
+
+# Azure Toolkit for IntelliJ plugin
+# https://plugins.jetbrains.com/plugin/8053-azure-toolkit-for-intellij
+.idea/**/azureSettings.xml
+
+# End of https://www.toptal.com/developers/gitignore/api/go,goland,dotenv

Dockerfile

@@ -0,0 +1,14 @@
+FROM golang:1.21-bullseye AS builder
+WORKDIR /src
+COPY . /src
+
+RUN go mod download
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags '-w -s' -o ./build/app ./main.go ./message.go
+
+FROM scratch
+
+COPY --from=builder /usr/share/zoneinfo/Asia/Tokyo /usr/share/zoneinfo/Asia/Tokyo
+COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
+
+COPY --from=builder /src/build/app /app
+ENTRYPOINT ["/app"]

go.mod

@@ -0,0 +1,13 @@
+module dns-mx-watchdog
+
+go 1.21
+
+require (
+	github.com/gorilla/websocket v1.4.2 // indirect
+	github.com/miekg/dns v1.1.56 // indirect
+	github.com/slack-go/slack v0.12.3 // indirect
+	golang.org/x/mod v0.12.0 // indirect
+	golang.org/x/net v0.15.0 // indirect
+	golang.org/x/sys v0.12.0 // indirect
+	golang.org/x/tools v0.13.0 // indirect
+)

go.sum

@@ -0,0 +1,20 @@
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-test/deep v1.0.4/go.mod h1:wGDj63lr65AM2AQyKZd/NYHGb0R+1RLqB8NKt3aSFNA=
+github.com/google/go-cmp v0.5.7/go.mod h1:n+brtR0CgQNWTVd5ZUFpTBC8YFBDLK/h/bpaJ8/DtOE=
+github.com/gorilla/websocket v1.4.2 h1:+/TMaTYc4QFitKJxsQ7Yye35DkWvkdLcvGKqM+x0Ufc=
+github.com/gorilla/websocket v1.4.2/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
+github.com/miekg/dns v1.1.56 h1:5imZaSeoRNvpM9SzWNhEcP9QliKiz20/dA2QabIGVnE=
+github.com/miekg/dns v1.1.56/go.mod h1:cRm6Oo2C8TY9ZS/TqsSrseAcncm74lfK5G+ikN2SWWY=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/slack-go/slack v0.12.3 h1:92/dfFU8Q5XP6Wp5rr5/T5JHLM5c5Smtn53fhToAP88=
+github.com/slack-go/slack v0.12.3/go.mod h1:hlGi5oXA+Gt+yWTPP0plCdRKmjsDxecdHxYQdlMQKOw=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+golang.org/x/mod v0.12.0 h1:rmsUpXtvNzj340zd98LZ4KntptpfRHwpFOHG188oHXc=
+golang.org/x/mod v0.12.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
+golang.org/x/net v0.15.0 h1:ugBLEUaxABaB5AJqW9enI0ACdci2RUd4eP51NTBvuJ8=
+golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
+golang.org/x/sys v0.12.0 h1:CM0HF96J0hcLAwsHPJZjfdNzs0gftsLfgKt57wWHJ0o=
+golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/tools v0.13.0 h1:Iey4qkscZuv0VvIt8E0neZjtPVQFSc870HQ448QgEmQ=
+golang.org/x/tools v0.13.0/go.mod h1:HvlwmtVNQAhOuCjW7xxvovg8wbNq7LwfXh/k7wXUl58=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

main.go

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+package main
+
+import (
+	"fmt"
+	"github.com/miekg/dns"
+	"github.com/slack-go/slack"
+	"log"
+	"os"
+	"time"
+)
+
+func main() {
+	token := os.Getenv("SLACK_BOT_TOKEN")
+	channelId := os.Getenv("CHANNEL_ID")
+
+	dnsServer := os.Getenv("DNS_SERVER")
+	domain := os.Getenv("DOMAIN")
+
+	client := slack.New(token)
+
+	ticker := time.NewTicker(time.Millisecond * 60 * 60 * 1000)
+	defer ticker.Stop()
+
+	log.Printf("DNS Watchdog task has been started")
+
+	count := 0
+	for {
+		select {
+		case <-ticker.C:
+			log.Printf("count=%d\n", count)
+			ok := lookupMXRecords(dnsServer, domain)
+			if ok {
+				count++
+				if count > 24 {
+					count = 0
+					SendDailyNotification(*client, channelId, dnsServer, domain)
+				}
+			} else {
+				count = 0
+				SendHourlyNotification(*client, channelId, dnsServer, domain)
+			}
+		}
+	}
+}
+
+func lookupMXRecords(dnsServer string, domain string) bool {
+	m := new(dns.Msg)
+	m.SetQuestion(domain+".", dns.TypeMX)
+
+	c := new(dns.Client)
+	in, _, err := c.Exchange(m, dnsServer)
+	if err != nil {
+		fmt.Println("DNS Query Failed:", err)
+		return false
+	}
+
+	for _, answer := range in.Answer {
+		if mx, ok := answer.(*dns.MX); ok {
+			fmt.Printf("Host: %s, Priority: %d\n", mx.Mx, mx.Preference)
+		}
+	}
+	return true
+}

message.go

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+package main
+
+import (
+	"fmt"
+	"github.com/slack-go/slack"
+	"log"
+	"time"
+)
+
+func SendDailyNotification(client slack.Client, channelId string, dnsServer string, domain string) {
+	attachment := slack.Attachment{
+		Title: "DNS MX Query Successful (daily report)",
+		Color: "good",
+
+		Fields: []slack.AttachmentField{
+			{
+				Title: "Domain",
+				Value: "*" + domain + "*",
+				Short: false,
+			}, {
+				Title: "DNS Server",
+				Value: "*" + dnsServer + "*",
+				Short: false,
+			},
+			{
+				Title: "Date & Time",
+				Value: time.Now().Format("2006/1/2 15:04"),
+				Short: false,
+			},
+		},
+	}
+
+	_, _, err := client.PostMessage(
+		channelId,
+		slack.MsgOptionAttachments(attachment),
+		slack.MsgOptionAsUser(true),
+	)
+	if err != nil {
+		fmt.Printf("%s\n", err)
+		return
+	}
+	log.Printf("[daily report] Message successfully sent to channel")
+}
+
+func SendHourlyNotification(client slack.Client, channelId string, dnsServer string, domain string) {
+	attachment := slack.Attachment{
+		Pretext: "<!channel>",
+		Title:   "DNS MX Query FAILED (hourly report)",
+		Color:   "danger",
+
+		Fields: []slack.AttachmentField{
+			{
+				Title: "Domain",
+				Value: "*" + domain + "*",
+				Short: false,
+			}, {
+				Title: "DNS Server",
+				Value: "*" + dnsServer + "*",
+				Short: false,
+			},
+			{
+				Title: "Date & Time",
+				Value: time.Now().Format("2006/1/2 15:04"),
+				Short: false,
+			},
+		},
+	}
+
+	_, _, err := client.PostMessage(
+		channelId,
+		slack.MsgOptionAttachments(attachment),
+		slack.MsgOptionAsUser(true),
+	)
+	if err != nil {
+		fmt.Printf("%s\n", err)
+		return
+	}
+	fmt.Printf("[hourly report] Message successfully sent to channel")
+}