NodeBB Scaling makes Mongodb Dead

[Dk]

i use this configure
https://docs.nodebb.org/configuring/scaling/
but after a few days nodebb dead
so i check service, found mongodb not running
the mongod log last line show nodebb get lots of post

2018-08-28T14:40:05.667+0800 I COMMAND  [conn28] command nodebb.objects command: getMore { getMore: 24796725858, collection: "objects", batchSize: 1000, lsid: { id: UUID("xxx") }, $readPreference: { mode: "secondaryPreferred" }, $db: "no
debb" } originatingCommand: { find: "objects", filter: { _key: { $in: [ "post:63437".......... "post:98592" ] } }, projection: { _id: 0 }, returnKey: false, showRecordId: false, lsid: { id: UUID("xxx") }, $db: "nodebb" } planSummary: IXSCAN { _key: 1, value: -1 } cursorid:24796725858 keysExamined:840 docsExamined:424 cursorExhausted:1 numYields:10 nreturned:424 reslen:163097 locks:{ Global: { acquireCount: { r: 11 } }, Database: { acquireCount: { r: 11 } }, Collection: { acquireCount: { r: 11 } } } protocol:op_query 242ms

the mongod config is from apt source

i want know what makes mongodb stop, not set daemon let it restart frequently

[baris]

Did you check /var/log/syslog to see if it was killed because of insufficient memory?

[Dk]

@baris only get this
Aug 28 16:39:27 hostname mongod[7590]: 2018-08-28T16:39:27.604+0800 I CONTROL [main] Automatically disabling TLS 1.0, to force-enable TLS 1.0 specify --sslDisabledProtocols 'none'

# free -m
              total        used        free      shared  buff/cache   available
Mem:           1735        1296         102           3         336         231
Swap:          1019         287         731

#/etc/mongod.conf
storage:
  dbPath: /var/lib/mongodb
  journal:
    enabled: true

systemLog:
  destination: file
  logAppend: true
  path: /var/log/mongodb/mongod.log

net:
  port: 27017
  bindIp: 127.0.0.1

processManagement:
  timeZoneInfo: /usr/share/zoneinfo

security:
  authorization: enabled