fix: prevent slice backing array corruption in docker metrics#151
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fix: prevent slice backing array corruption in docker metrics#151
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Multiple append() calls on the shared labelNames slice could share the same underlying backing array, causing label names to be overwritten. This resulted in a panic: "label name 'device_major' missing in label map" when Prometheus tried to use network metrics with corrupted labels. Create dedicated label slices for network and block I/O metrics using make() with explicit capacity, following the pattern already used for volume metrics in the same file.
samcm
approved these changes
Jan 14, 2026
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Summary
label name "device_major" missing in label mapin docker metrics collectionappend()calls on sharedlabelNamesslice corrupted label definitions due to backing array sharingmake()with explicit capacityDetails
The bug was latent but became visible after the Go 1.25 upgrade. Go's slice growth algorithm changed, causing
labelNamesto retain extra capacity after initial building. Subsequentappend(labelNames, "interface")andappend(labelNames, "device_major", "device_minor")calls then shared the same backing array, with block I/O labels overwriting network labels.The fix follows the same safe pattern already used for volume metrics in the same file.
Logs
Test plan
go build ./...)go test ./...)