[BUG] Persistent "field auth not found in type config.plain" error with v0.27.0 and v0.28.0

[iamtinu]

The core issue is a persistent and contradictory error preventing the snmp_exporter Docker container from starting, despite all configuration and execution steps aligning with official documentation and best practices.

Specifically:
Error Message: The snmp_exporter continuously fails with the error message: yaml: unmarshal errors: line X: field auth not found in type config.plain. The line number varies depending on the snmp.yml format used.

Configuration Contradiction:
When using snmp_exporter:v0.28.0 with its new configuration format (top-level auths section), the exporter reports this error and suggests a "version mismatch" with a link to the auth-split-migration.md guide. This is contradictory, as v0.28.0 is precisely the version that requires this new format.

When reverting to snmp_exporter:v0.27.0 and its corresponding old configuration format (nested auth directly under modules), the exact same field auth not found in type config.plain error persists, which is also contradictory to v0.27.0's expected behavior.

Debugging Efforts Exhausted:
Multiple snmp_exporter image versions (v0.28.0, v0.27.0) have been tested.
Both the new and old snmp.yml configuration formats have been applied and verified to match the respective exporter versions.

Docker caches have been cleared thoroughly.
Interactive debugging inside the container confirmed that the snmp.yml file is correctly mounted and its content is as expected by the cat command.

Manual execution of the snmp_exporter binary directly within the container (after locating its correct path at /bin/snmp_exporter) produced the identical yaml: unmarshal errors message, ruling out Docker Compose or entrypoint issues.

Logs from the container itself

root@grafana-62:~/prom# docker run -it --rm   -v "$(pwd)"/snmp-exporter/snmp.yml:/etc/snmp_exporter/snmp.yml:ro   --name snmp_exporter_debug   --entrypoint sh   prom/snmp-exporter:v0.28.0
/ # which snmp_exporter
/bin/snmp_exporter
/ # find / -name snmp_exporter 2>/dev/null
/etc/snmp_exporter
/bin/snmp_exporter
/ # /bin/snmp_exporter --config.file=/etc/snmp_exporter/snmp.yml --log.level=debug
time=2025-07-07T11:05:45.749Z level=INFO source=main.go:211 msg="Starting snmp_exporter" version="(version=0.28.0, branch=HEAD, revision=9f9547f664b61449281ff888fe690c68ef94c9f2)" concurrency=0xc0000131b0 debug_snmp=0xc0000131b8
time=2025-07-07T11:05:45.749Z level=INFO source=main.go:212 msg="operational information" build_context="(go=go1.23.6, platform=linux/amd64, user=root@cff6a587972e, date=20250207-00:00:24, tags=unknown)"
time=2025-07-07T11:05:45.749Z level=ERROR source=main.go:219 msg="Error parsing config file" err="yaml: unmarshal errors:\n  line 12: field auth not found in type config.plain"
time=2025-07-07T11:05:45.749Z level=ERROR source=main.go:220 msg="Possible version missmatch between generator and snmp_exporter. Make sure generator and snmp_exporter are the same version."
time=2025-07-07T11:05:45.749Z level=ERROR source=main.go:221 msg="See also: https://github.com/prometheus/snmp_exporter/blob/main/auth-split-migration.md"

Tried 2 and 2c both on 0.27.0 and 0.28.0

root@grafana-62:~/prom# docker logs snmp_exporter
time=2025-07-07T10:54:56.112Z level=INFO source=main.go:211 msg="Starting snmp_exporter" version="(version=0.28.0, branch=HEAD, revision=9f9547f664b61449281ff888fe690c68ef94c9f2)" concurrency=0xc0000ae030 debug_snmp=0xc0000ae038
time=2025-07-07T10:54:56.112Z level=INFO source=main.go:212 msg="operational information" build_context="(go=go1.23.6, platform=linux/amd64, user=root@cff6a587972e, date=20250207-00:00:24, tags=unknown)"
time=2025-07-07T10:54:56.112Z level=ERROR source=main.go:219 msg="Error parsing config file" err="yaml: unmarshal errors:\n  line 4: cannot unmarshal !!str `2c` into int\n  line 12: field auth not found in type config.plain"
time=2025-07-07T10:54:56.112Z level=ERROR source=main.go:220 msg="Possible version missmatch between generator and snmp_exporter. Make sure generator and snmp_exporter are the same version."
time=2025-07-07T10:54:56.112Z level=ERROR source=main.go:221 msg="See also: https://github.com/prometheus/snmp_exporter/blob/main/auth-split-migration.md"
root@grafana-62:~/prom# docker compose up -d --force-recreate snmp_exporter
[+] Running 1/1
 ✔ Container snmp_exporter  Started                                                                                                                                                                                                   0.3s
root@grafana-62:~/prom# docker ps
CONTAINER ID   IMAGE                                      COMMAND                  CREATED              STATUS              PORTS                                         NAMES
426d7af67e7f   grafana/grafana:latest                     "/run.sh"                About a minute ago   Up About a minute   0.0.0.0:3000->3000/tcp, [::]:3000->3000/tcp   grafana
ac771f7946ef   prom/prometheus:latest                     "/bin/prometheus --c…"   About a minute ago   Up About a minute   0.0.0.0:9090->9090/tcp, [::]:9090->9090/tcp   prometheus
ff055a23ee28   prometheuscommunity/ipmi-exporter:latest   "/bin/ipmi_exporter …"   About a minute ago   Up About a minute   0.0.0.0:9290->9290/tcp, [::]:9290->9290/tcp   ipmi_exporter
fe202bb54371   mongo:4.4                                  "docker-entrypoint.s…"   3 days ago           Up 3 days           27017/tcp                                     cosmos-mongo-4p6
root@grafana-62:~/prom# docker logs snmp_exporter
time=2025-07-07T10:56:22.413Z level=INFO source=main.go:211 msg="Starting snmp_exporter" version="
(version=0.28.0, branch=HEAD, revision=9f9547f664b61449281ff888fe690c68ef94c9f2)" concurrency=0xc0000a3140 debug_snmp=0xc0000a3148
time=2025-07-07T10:56:22.413Z level=INFO source=main.go:212 msg="operational information" build_context="(go=go1.23.6, platform=linux/amd64, user=root@cff6a587972e, date=20250207-00:00:24, tags=unknown)"
time=2025-07-07T10:56:22.413Z level=ERROR source=main.go:219 msg="Error parsing config file" err="yaml: unmarshal errors:\n  line 12: field auth not found in type config.plain"
time=2025-07-07T10:56:22.414Z level=ERROR source=main.go:220 msg="Possible version missmatch between generator and snmp_exporter. Make sure generator and snmp_exporter are the same version."
time=2025-07-07T10:56:22.414Z level=ERROR source=main.go:221 msg="See also: https://github.com/prometheus/snmp_exporter/blob/main/auth-split-migration.md"

[SuperQ]

You don't include your snmp.yml, so it's impossible to tell you what's wrong.

[iamtinu]

# ~/prom/snmp-exporter/snmp.yml
auths:
  idrac_auth: # A custom name for authentication configuration
    version: 2c
    community: "alm0znin0" # SNMP community string

modules:
  dell_power: # New module for Dell power monitoring
    walk:
      - 1.3.6.1.2.1.1 # System MIB (basic info, already there)
      - 1.3.6.1.4.1.674.10892.5.4.300.10.1.10.1 # Dell System Power Consumption in Watts (found from snmpwalk)
    auth: idrac_auth # Reference the named authentication configuration

# ~/prom/snmp-exporter/snmp.yml
# Removed the top-level 'auths' section

modules:
  dell_power: # This module name must match 'module' in prometheus.yml
    walk:
      - 1.3.6.1.2.1.1 # System MIB (basic info)
      - 1.3.6.1.4.1.674.10892.5.4.300.10.1.10.1 # Dell System Power Consumption in Watts
    auth: # <--- This 'auth' is now directly under 'dell_power'
      version: 2
      community: "alm0znin0" # SNMP community string

I tried these two plus other variations as well