From f49fac079893d79d1ccbb40df67c1ae2e0705c2c Mon Sep 17 00:00:00 2001
From: Alvar Penning <alvar.penning@icinga.com>
Date: Mon, 26 Aug 2024 09:44:56 +0200
Subject: [PATCH] CheckSchema: Verify intermediate schema upgrades

When skipping a version for an Icinga DB upgrade, all intermediate
upgrade steps must be taken. While this is already stated in the
documentation, it might be overlooked.

This happened for one community user, upgrading from v1.1.0 to v1.2.0,
skipping the intermediate schema upgrade for v1.1.1.

> https://community.icinga.com/t/icingadb-failing-exactly-5-minutes-after-start/13955

First, the necessity for all upgrades in their release order was made
more prominent in the documentation, hoping that less users would ignore
this when skimming the upgrade docs.

However, the real change here is adding another check to the CheckSchema
function, verifying that all schema upgrades between the lowest known
version and the highest known version in the icingadb_schema table
exists. If an intermediate schema upgrade was skipped, as in the thread
above, this raises a descriptive error.
---
 doc/04-Upgrading.md    |  3 ++-
 pkg/icingadb/schema.go | 27 ++++++++++++++++++++++-----
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/doc/04-Upgrading.md b/doc/04-Upgrading.md
index 00bb6bd4..c2af5c15 100644
--- a/doc/04-Upgrading.md
+++ b/doc/04-Upgrading.md
@@ -4,7 +4,8 @@ Some Icinga DB upgrades require manual intervention, others do not. If you need
 point you to the specific upgrade section on this page.
 
 Please note that version upgrades are incremental. If you are upgrading across multiple versions, make sure to follow
-the steps for each of them.
+the steps for each of them. For example, when upgrading from version 1.1.0 to 1.2.0, follow all instructions for
+upgrading to 1.1.1, then all for 1.2.0, including schema upgrades.
 
 ## Database Schema Upgrades
 
diff --git a/pkg/icingadb/schema.go b/pkg/icingadb/schema.go
index 47dd1d13..d78a8957 100644
--- a/pkg/icingadb/schema.go
+++ b/pkg/icingadb/schema.go
@@ -48,12 +48,13 @@ func CheckSchema(ctx context.Context, db *database.DB) error {
 		return ErrSchemaNotExists
 	}
 
-	var version uint16
+	var versions []uint16
+
 	err := retry.WithBackoff(
 		ctx,
 		func(ctx context.Context) error {
-			query := "SELECT version FROM icingadb_schema ORDER BY id DESC LIMIT 1"
-			if err := db.QueryRowxContext(ctx, query).Scan(&version); err != nil {
+			query := "SELECT version FROM icingadb_schema ORDER BY version ASC"
+			if err := db.SelectContext(ctx, &versions, query); err != nil {
 				return database.CantPerformQuery(err, query)
 			}
 			return nil
@@ -65,12 +66,28 @@ func CheckSchema(ctx context.Context, db *database.DB) error {
 		return errors.Wrap(err, "can't check database schema version")
 	}
 
-	if version != expectedDbSchemaVersion {
+	if len(versions) == 0 {
+		return fmt.Errorf("%w: no database schema version is stored in the database", ErrSchemaMismatch)
+	}
+
+	// Check if each schema update between the initial import and the latest version was applied or, in other words,
+	// that no schema update was left out. The loop goes over the ascending sorted array of schema versions, verifying
+	// that each element's successor is the increment of this version, ensuring no gaps in between.
+	for i := 0; i < len(versions)-1; i++ {
+		if versions[i] != versions[i+1]-1 {
+			return fmt.Errorf(
+				"%w: incomplete database schema upgrade: intermediate version v%d is missing,"+
+					" please make sure you have applied all database migrations after upgrading Icinga DB",
+				ErrSchemaMismatch, versions[i]+1)
+		}
+	}
+
+	if latestVersion := versions[len(versions)-1]; latestVersion != expectedDbSchemaVersion {
 		// Since these error messages are trivial and mostly caused by users, we don't need
 		// to print a stack trace here. However, since errors.Errorf() does this automatically,
 		// we need to use fmt instead.
 		return fmt.Errorf("%w: v%d (expected v%d), please make sure you have applied all database"+
-			" migrations after upgrading Icinga DB", ErrSchemaMismatch, version, expectedDbSchemaVersion,
+			" migrations after upgrading Icinga DB", ErrSchemaMismatch, latestVersion, expectedDbSchemaVersion,
 		)
 	}