feat: scheduled healthchecks with reporting via Discord webhook

.gitignore

@@ -7,6 +7,8 @@ yarn-error.log*
 lerna-debug.log*
 .pnpm-debug.log*
 
+config.json
+
 # Diagnostic reports (https://nodejs.org/api/report.html)
 report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json
 
@@ -128,3 +130,6 @@ dist
 .yarn/build-state.yml
 .yarn/install-state.gz
 .pnp.*
+
+# Local Netlify folder
+.netlify

.yarnrc.yml

@@ -0,0 +1 @@
+nodeLinker: node-modules

README.md

@@ -1,2 +1,18 @@
 # healthcheck
 Personal DiscordOps to keep things I deploy in check
+
+## Configuration
+
+A configuration file should be manually pushed and made accessible to the functions. This can be done via `netlify blobs:set test config -i ./config.json` provided that `config.json` has content that matches the configuration schema:
+
+```
+{
+  "endpoints": [
+    { "name": <service-name>, "url": <endpoint-url> },
+    ...
+  ],
+  "webhook_url": <webhook-url>
+}
+```
+
+The `webhook-url` is expected to contain `$DISCORD_WEBHOOK_ID` and `$DISCORD_WEBHOOK_TOKEN` placeholders.

netlify.toml

@@ -0,0 +1,8 @@
+[build]
+    publish = "."
+
+[functions]
+    directory = "src/"
+
+[functions."scheduledHealthcheck"]
+    schedule = "*/10 * * * *"

package.json

@@ -0,0 +1,18 @@
+{
+  "name": "healthcheck",
+  "version": "noversion",
+  "main": "index.js",
+  "repository": "git@github.com:mcataford/healthcheck.git",
+  "author": "Marc Cataford <mcat@riseup.net>",
+  "private": true,
+  "packageManager": "yarn@4.1.1",
+  "devDependencies": {
+    "@types/node": "^20.11.27",
+    "typescript": "^5.4.2"
+  },
+  "dependencies": {
+    "@netlify/blobs": "^7.0.1",
+    "@netlify/functions": "^2.6.0",
+    "axios": "^1.6.7"
+  }
+}

src/scheduledHealthcheck.mts

@@ -0,0 +1,85 @@
+import { readFile } from 'node:fs/promises'
+
+import axios from 'axios'
+import { getStore } from '@netlify/blobs'
+import type { Context } from '@netlify/functions'
+
+interface Endpoint {
+    name: string
+    url: string
+}
+
+interface Configuration {
+    endpoints: Endpoint[]
+    webhook_url: string
+}
+
+interface EndpointReport extends Endpoint {
+    status: number
+    healthy: boolean
+}
+
+/*
+ * Sends a GET request to the specified Endpoint url and reports on whether
+ * the response given back was a success or not.
+ *
+ * Any error when handling the request (request-related or not) is deemed
+ * to be a failing ping.
+ *
+ * Returns an EndpointReport, which is the Endpoint used as input with
+ * extra status information.
+ */
+async function pingEndpoint(endpoint: Endpoint): Promise<EndpointReport> {
+    try {
+        const response = await axios.get(endpoint.url)
+    
+        return {
+            ...endpoint,
+            status: response.status,
+            healthy: true
+        }
+    } catch(e) {
+        return {
+            ...endpoint,
+            healthy: false,
+            status: e.response.status
+        }
+    }
+}
+
+/*
+ * Formats endpoint reports into a string that can be posted to the Discord webhook.
+ *
+ * The report is assembled line-by-line and joined together as one.
+ */
+function formatReport(endpointReports: EndpointReport[]): string {
+    const endpointStatuses = endpointReports.map((report: EndpointReport): string => {
+        if (report.healthy)
+            return `✅ ${report.name} is healthy (${report.status})`
+        else
+            return `🔥 ${report.name} did not respond normally (${report.status})`
+    })
+
+    return endpointStatuses.join('\n')
+}
+
+/*
+ * Pings all endpoints configured to be healthchecked and sends a report on the success/failure
+ * of requests to the Discord webhook included in the configuration.
+ *
+ * This expects DISCORD_WEBHOOK_ID and DISCORD_WEBHOOK_TOKEN to be configured through
+ * the available environment variables separately.
+ */
+export default async (request: Request, context: Context) => {
+    //const conf: Configuration = require("../config.json")
+    const configurationStore = getStore('functions')
+    const conf: Configuration = await configurationStore.get('config', { type: 'json' })
+
+    const pings = await Promise.all(conf.endpoints.map(pingEndpoint))
+
+    const report = formatReport(pings)
+    const webhook_url = conf.webhook_url.replace('$DISCORD_WEBHOOK_ID', process.env.DISCORD_WEBHOOK_ID).replace('$DISCORD_WEBHOOK_TOKEN', process.env.DISCORD_WEBHOOK_TOKEN)
+    await axios.post(webhook_url, { content: report })
+
+    return new Response()
+}

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