From 44ebf12d257e4e1fcfb709ea0727748eeff012fc Mon Sep 17 00:00:00 2001
From: David Mehren <git@herrmehren.de>
Date: Tue, 4 May 2021 18:25:30 +0200
Subject: [PATCH] Automatically retry DB connection on startup

This adds retry logic to the initial DB connection on startup.
HedgeDoc now tries connecting to the database up to 30 times, waiting
one second after each try.
This gives a database that was simultaneously started (e.g. via
docker-compose) enough time to get ready to accept connections.

Signed-off-by: David Mehren <git@herrmehren.de>
---
 app.js | 41 +++++++++++++++++++++++++++++------------
 1 file changed, 29 insertions(+), 12 deletions(-)

diff --git a/app.js b/app.js
index beb0743b9..da1c8e9c0 100644
--- a/app.js
+++ b/app.js
@@ -272,21 +272,38 @@ function startListen () {
   }
 }
 
-// sync db then start listen
-models.sequelize.authenticate().then(function () {
-  models.runMigrations().then(() => {
-    sessionStore.sync()
-    // check if realtime is ready
-    if (realtime.isReady()) {
-      models.Revision.checkAllNotesRevision(function (err, notes) {
-        if (err) throw new Error(err)
-        if (!notes || notes.length <= 0) return startListen()
-      })
+const maxDBTries = 30
+let currentDBTry = 1
+function syncAndListen () {
+  // sync db then start listen
+  models.sequelize.authenticate().then(function () {
+    models.runMigrations().then(() => {
+      sessionStore.sync()
+      // check if realtime is ready
+      if (realtime.isReady()) {
+        models.Revision.checkAllNotesRevision(function (err, notes) {
+          if (err) throw new Error(err)
+          if (!notes || notes.length <= 0) return startListen()
+        })
+      } else {
+        logger.error('server still not ready after db synced')
+        process.exit(1)
+      }
+    })
+  }).catch(() => {
+    if (currentDBTry < maxDBTries) {
+      logger.warn(`Database cannot be reached. Try ${currentDBTry} of ${maxDBTries}.`)
+      currentDBTry++
+      setTimeout(function () {
+        syncAndListen()
+      }, 1000)
     } else {
-      throw new Error('server still not ready after db synced')
+      logger.error('Cannot reach database! Exiting.')
+      process.exit(1)
     }
   })
-})
+}
+syncAndListen()
 
 // log uncaught exception
 process.on('uncaughtException', function (err) {