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fix: Preserve mongo_db_major_version state after out-of-band major version upgrade #4400

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fix: Preserve mongo_db_major_version state after out-of-band major version upgrade #4400

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32ca815
fix: preserve api mongo_db_major_version on real upgrades
mkusaka Apr 23, 2026
93cbb4d
Fix lint issue by using correct package and update function to give a…
marcabreracast Apr 23, 2026
5d1bfd1
Add changelog
marcabreracast Apr 23, 2026
0b83ff7
Rename file due to typo and address PR comments
marcabreracast Apr 23, 2026
e3afc28
Add case to use major component comparison to avoid inconsistency errors
marcabreracast Apr 23, 2026
dab5e4b
Rephrase changelog for clarity
marcabreracast Apr 24, 2026
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3 changes: 3 additions & 0 deletions .changelog/4400.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
```release-note:bug
resource/mongodbatlas_advanced_cluster: Fixes perpetual plan drift on `mongo_db_major_version` after out-of-band major version upgrade
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```
42 changes: 42 additions & 0 deletions internal/service/advancedcluster/resource_compatibility_test.go
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package advancedcluster_test
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import (
"testing"

"github.com/mongodb/terraform-provider-mongodbatlas/internal/service/advancedcluster"
"github.com/stretchr/testify/assert"
)

func TestAdvancedCluster_ShouldUsePreviousMongoDBMajorVersion(t *testing.T) {
testCases := []struct {
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@augmentcode augmentcode Bot Apr 24, 2026 •
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internal/service/advancedcluster/resource_compatibility_test.go:11 — The table covers major-change vs same-major outcomes, but it doesn’t exercise the beforeVersion == afterVersion early-return branch in ShouldUsePreviousMongoDBMajorVersion. Consider adding an explicit equality case to lock in that behavior.

Severity: low

Fix This in Augment

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name string
before string
after string
expected bool
}{
{
name: "keeps previous version when only formatting differs",
before: "8",
after: "8.0",
expected: true,
},
{
name: "uses API value when major version actually changed",
before: "7.0",
after: "8.0",
expected: false,
},
{
name: "keeps previous version when minor version differs within same major",
before: "8.0",
after: "8.2",
expected: true,
},
}

for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
assert.Equal(t, tc.expected, advancedcluster.ShouldUsePreviousMongoDBMajorVersion(tc.before, tc.after))
})
}
}
17 changes: 16 additions & 1 deletion internal/service/advancedcluster/resource_compatiblity.go
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Expand Up @@ -4,6 +4,7 @@ import (
"context"
"fmt"
"strconv"
"strings"

"go.mongodb.org/atlas-sdk/v20250312018/admin"

Expand Down Expand Up @@ -94,7 +95,9 @@ func overrideAttributesWithPrevStateValue(modelIn, modelOut *TFModel) {
return
}
beforeVersion := conversion.NilForUnknown(modelIn.MongoDBMajorVersion, modelIn.MongoDBMajorVersion.ValueStringPointer())
if beforeVersion != nil && !modelIn.MongoDBMajorVersion.Equal(modelOut.MongoDBMajorVersion) {
afterVersion := conversion.NilForUnknown(modelOut.MongoDBMajorVersion, modelOut.MongoDBMajorVersion.ValueStringPointer())
// Only preserve prior state value for formatting differences (e.g. "8" vs "8.0"), not real version transitions.
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@augmentcode augmentcode Bot Apr 24, 2026 •
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internal/service/advancedcluster/resource_compatiblity.go:99 — This comment says the override is only for formatting differences, but ShouldUsePreviousMongoDBMajorVersion also preserves the prior value when the minor version changes within the same major (e.g., CONTINUOUS returning 8.2). Consider clarifying the comment so future readers don’t assume this logic is formatting-only.

Severity: low

Fix This in Augment

🤖 Was this useful? React with 👍 or 👎, or 🚀 if it prevented an incident/outage.

if beforeVersion != nil && afterVersion != nil && ShouldUsePreviousMongoDBMajorVersion(*beforeVersion, *afterVersion) {
modelOut.MongoDBMajorVersion = types.StringPointerValue(beforeVersion)
}
overrideMapStringWithPrevStateValue(&modelIn.Labels, &modelOut.Labels)
Expand All @@ -109,6 +112,18 @@ func overrideAttributesWithPrevStateValue(modelIn, modelOut *TFModel) {
modelOut.UseEffectiveFields = modelIn.UseEffectiveFields
}

func ShouldUsePreviousMongoDBMajorVersion(beforeVersion, afterVersion string) bool {
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@marcabreracast marcabreracast Apr 24, 2026

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This function helps preserve the prior state value when the major component is the same, which handles two cases:

  1. Formatting differences: user sets "8" but Atlas returns "8.0" which is the same version, but different format. This is to preserve SDKv2 behaviour
  2. version_release_system = "CONTINUOUS": Atlas can return a minor bump (e.g. "8.2") that is not user-controlled. Letting it through causes: provider produced an unexpected new value: .mongo_db_major_version: was cty.StringVal("8.0"), but now cty.StringVal("8.2"). `

The reason why step 2 is implemented, is to avoid unit test failure

if beforeVersion == afterVersion {
return false
}
return majorComponent(beforeVersion) == majorComponent(afterVersion)
}

func majorComponent(version string) string {
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@AgustinBettati AgustinBettati Apr 24, 2026

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Users that have an outdate mongo_db_major_version value would now receive a non-empty plan (cases where major version upgrade was done outside of TF). Would confirm with Alex we are okay with this impact.

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@AgustinBettati AgustinBettati Apr 24, 2026

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q: Does version_release_system = "CONTINUOUS" only upgrade minor versions?

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@marcabreracast marcabreracast Apr 24, 2026

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Both, per my understanding of the docs:

Latest Version With Auto Upgrades: If you set your cluster to this release option, it receives automatic upgrades to the latest available MongoDB major or minor version

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@AgustinBettati AgustinBettati Apr 27, 2026

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Okay, would make sure to test if an error is returned if version_release_system = "CONTINUOUS" and mongo_db_major_version attribute are used together (as per our docs). Using this combination would lead to non-empty plan once automatic major version upgrades are made.

major, _, _ := strings.Cut(FormatMongoDBMajorVersion(version), ".")
return major
}

func overrideMapStringWithPrevStateValue(mapIn, mapOut *types.Map) {
if mapIn == nil || mapOut == nil || len(mapOut.Elements()) > 0 {
return
Expand Down