SNMP: multiple hosts on same port collide snmpwalk namespace

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    • Type: Bug
    • Resolution: Won't Fix
    • Priority: Major - P3
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    • Affects Version/s: 2.5.3
    • Component/s: Diagnostics
    • Environment:
      * EC2, Amazon Linux, m1.medium
      * PSS replica set
      * All mongod instances running as SNMP subagents, reporting to {{snmpd}} functioning as SNMP master
    • ALL
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      0.) Install standard pre-req packages for SNMP.
      1.) Edit /etc/snmp/snmpd.conf and /etc/snmp/mongod.conf config files for subagent connection to snmpd through TCP:1705.
      2.) Start up snmpd daemon.
      3.) Launch a PSS replica set, with each running with --snmp-subagent on a distinct host and same port.
      3.) Run snmpwalk against the agentaddress defined for your running snmpd daemon
      snmpwalk -m MONGO-MIB -v 2c -c mongodb ec2-foo-bar.amazonaws.com:1161 1.3.6.1.4.1.34601

      Actual command-line flags used for each host:
      PRI: ./bin/mongod --replSet snmpd --snmp-subagent --port 27017 --fork --dbpath data/snmpd-0/ --logpath logs/snmpd-0/mongod.log --smallfiles --nohttpinterface --oplogSize=50

      SEC: ./bin/mongod --replSet snmpd --snmp-subagent --port 27017 --fork --dbpath data/snmpd-2/ --logpath logs/snmpd-2/mongod.log --smallfiles --nohttpinterface --oplogSize=50

      SEC: ./bin/mongod --replSet snmpd --snmp-subagent --port 27017 --fork --dbpath data/snmpd-4/ --logpath logs/snmpd-4/mongod.log --smallfiles --nohttpinterface --oplogSize=50

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      0.) Install standard pre-req packages for SNMP. 1.) Edit /etc/snmp/snmpd.conf and /etc/snmp/mongod.conf config files for subagent connection to snmpd through TCP:1705. 2.) Start up snmpd daemon. 3.) Launch a PSS replica set, with each running with --snmp-subagent on a distinct host and same port. 3.) Run snmpwalk against the agentaddress defined for your running snmpd daemon snmpwalk -m MONGO-MIB -v 2c -c mongodb ec2-foo-bar.amazonaws.com:1161 1.3.6.1.4.1.34601 Actual command-line flags used for each host: PRI: ./bin/mongod --replSet snmpd --snmp-subagent --port 27017 --fork --dbpath data/snmpd-0/ --logpath logs/snmpd-0/mongod.log --smallfiles --nohttpinterface --oplogSize=50 SEC: ./bin/mongod --replSet snmpd --snmp-subagent --port 27017 --fork --dbpath data/snmpd-2/ --logpath logs/snmpd-2/mongod.log --smallfiles --nohttpinterface --oplogSize=50 SEC: ./bin/mongod --replSet snmpd --snmp-subagent --port 27017 --fork --dbpath data/snmpd-4/ --logpath logs/snmpd-4/mongod.log --smallfiles --nohttpinterface --oplogSize=50
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      If a replica set of SNMP subagents are all running on the same port on different hosts, then SNMP responses are ambiguous - only one "27017" entry is returned, and for which member appears to be arbitrary.

      ...
MONGO-MIB::globalOpInsert."27017" = Counter32: 1
MONGO-MIB::globalOpQuery."27017" = Counter32: 60
MONGO-MIB::globalOpUpdate."27017" = Counter32: 1
MONGO-MIB::globalOpDelete."27017" = Counter32: 0
...
MONGO-MIB::replSetName."27017" = STRING: "snmpd"
MONGO-MIB::replSetVersion."27017" = INTEGER: 3
MONGO-MIB::replIsMaster."27017" = INTEGER: 1
MONGO-MIB::replIsSecondary."27017" = INTEGER: 0
MONGO-MIB::replPrimary."27017" = STRING: "hostA:27017"
MONGO-MIB::replMe."27017" = STRING: "hostA:27017"

      Furthermore, if the replica set member identified by the MONGO-MIB::replMe field is brought down (in the above example, say hostA:27017 becomes unavailable), then the snmpwalk becomes unresponsive - does not return any results from any of the other members.

      This behavior would seem to limit the utility of the subagent model given a "typical" replica set deployment. However of course a workaround exists to always utilize a distinct set of ports when using SNMP.

            Assignee:
            Unassigned
            Reporter:
            John Morales (Inactive)
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              Created:
              Updated:
              Resolved: