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Fix inverted mongodb_mongos_sharding_chunks_is_balancer_running gauge #1295

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Fix inverted mongodb_mongos_sharding_chunks_is_balancer_running gauge #1295

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ed07046
Fix invertedmongodb_mongos_sharding_chunks_is_balancer_running gauge
nisarg14 May 28, 2026
7a9538c
Merge branch 'main' into fix/in-balancer-round-metric
ademidoff Jun 1, 2026
9c0c952
Merge branch 'main' into fix/in-balancer-round-metric
ademidoff Jun 1, 2026
933863b
extracted bool->value mapping in pure function and added unit test fo…
nisarg14 Jun 2, 2026
fd2a010
Fix field reference casing in chunksBalancerRunning
nisarg14 Jun 6, 2026
9d53c82
Update exporter/v1_compatibility_test.go
ademidoff Jun 16, 2026
16320bf
format source code for Fix inverted mongodb_mongos_sharding_chunks_is…
nisarg14 Jun 18, 2026
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12 changes: 8 additions & 4 deletions exporter/v1_compatibility.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1165,6 +1165,13 @@ func shardedCollectionsTotal(ctx context.Context, client *mongo.Client) (prometh
return prometheus.NewConstMetric(d, prometheus.GaugeValue, float64(collCount))
}

func balancerRunningValue(inBalancerRound bool) float64 {
if inBalancerRound {
return 1
}
return 0
}

func chunksBalancerRunning(ctx context.Context, client *mongo.Client) (prometheus.Metric, error) {
var m struct {
InBalancerRound bool `bson:"inBalancerRound"`
Expand All @@ -1177,10 +1184,7 @@ func chunksBalancerRunning(ctx context.Context, client *mongo.Client) (prometheu
return nil, err
}

value := float64(0)
if !m.InBalancerRound {
value = 1
}
value := balancerRunningValue(m.InBalancerRound)

name := "mongodb_mongos_sharding_chunks_is_balancer_running"
help := "Shard balancer is in a balancing round"
Expand Down
64 changes: 63 additions & 1 deletion exporter/v1_compatibility_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -211,9 +211,38 @@ func TestCreateOldMetricFromNew(t *testing.T) {
assert.Equal(t, want, nm)
}

func TestBalancerRunningValue(t *testing.T) {
t.Parallel()

tests := []struct {
name string
inBalancerRound bool
expected float64
}{
{
name: "balancer running",
inBalancerRound: true,
expected: 1,
},
{
name: "balancer not running",
inBalancerRound: false,
expected: 0,
},
}

for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
t.Parallel()
got := balancerRunningValue(tt.inBalancerRound)
assert.Equal(t, tt.expected, got)
})
}
}

func TestMongosMetrics(t *testing.T) {
t.Parallel()
t.Run("test mongodb_mongos_sharding_chunks_is_balancer_running metric", func(t *testing.T) {
t.Run("test mongodb_mongos_sharding_balancer_enabled metric", func(t *testing.T) {
type bss struct {
Mode string `bson:"mode"`
}
Expand Down Expand Up @@ -245,6 +274,39 @@ func TestMongosMetrics(t *testing.T) {
}
assert.Equal(t, float64(expected), m.GetGauge().GetValue()) //nolint
})

t.Run("test mongodb_mongos_sharding_chunks_is_balancer_running metric", func(t *testing.T) {
type bss struct {
InBalancerRound bool `bson:"inBalancerRound"`
}

t.Parallel()
ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
defer cancel()

port, err := tu.PortForContainer("mongos")
require.NoError(t, err)
client := tu.TestClient(ctx, port, t)

var bs bss
cmd := bson.D{{Key: "balancerStatus", Value: "1"}}
err = client.Database("admin").RunCommand(ctx, cmd).Decode(&bs)
require.NoError(t, err)

var metric prometheus.Metric
var m dto.Metric
metric, err = chunksBalancerRunning(ctx, client)
assert.NoError(t, err)

err = metric.Write(&m)
assert.NoError(t, err)

expected := 0
if bs.InBalancerRound {

@ademidoff ademidoff Jun 1, 2026

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This expected computation mirrors the function under test exactly (chunksBalancerRunning applies the same if inBalancerRound { 1 } mapping), so the assertion is tautological. It does guard against a re-introduced ! inversion, but on an idle test cluster inBalancerRound is effectively always false, so only the → 0 path is ever exercised — the → 1 path (the behavior this PR fixes) is never covered. Consider extracting the bool→value mapping into a pure function and unit-testing both inputs, or at minimum add a comment noting this limitation.

@nisarg14 nisarg14 Jun 2, 2026

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Thanks for the feedback. I’ve now extracted the bool->value mapping into a pure function and added a unit test covering both true and false cases. The integration test is kept only to verify the MongoDB response->metric wiring.

@ademidoff ademidoff Jun 16, 2026

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Awesome. One final fix - let's run make format, commit and push - it should make the linter happy :)

@nisarg14 nisarg14 Jun 19, 2026 •
edited
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Sure, i've ran make format and pushed the code

@nisarg14 nisarg14 Jul 9, 2026

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Gentle reminder @ademidoff i've ran the command can you please review

expected = 1
}
assert.Equal(t, float64(expected), m.GetGauge().GetValue()) //nolint
})
}

// myState should always return a metric. If there is no connection, the value
Expand Down