Error decoding JSON and broken logs in Elastic search - elasticsearch

Question

i'm using elk stack of version 5.5 in ubuntu 16.0
My logs are getting broken and not writting properly into elastic which is resulting in json.erros
like below
Error decoding JSON: invalid character 'e' in literal null (expecting 'u')"
getting json.errors very frequent and those logs are not reading or writting properly into elasticsearch ?
and this is happening for every 5 to 10 mins. please help me solve it.
screenshot of broken logs in kibana
My sample log is :
{"log":"2019-10-01 07:18:26:854*[DEBUG]*cluster2-nio-worker-0*Connection*userEventTriggered*Connection[cassandraclient/10.3.254.137:9042-1, inFlight=0, closed=false] was inactive for 30 seconds, sending heartbeat\n","stream":"stdout","time":"2019-10-01T07:18:26.85462769Z"}

Answer 1

Since you have stated that the json logs are not pretty printed I assume that the multiline-settings of your input configuration are causing the problems.
In my opinion you don't need any multiline settings when you have logs in json format and they are not pretty printed, meaning the whole json object (= log event) is written in one line.
You have already specified
json.message_key: log
This solely should get the job done.
So to sum it up:
Remove the multiline settings and try again. Your configuration should look like this:
filebeat.inputs:
- type: log
paths:
- "/var/log/containers/*.log"
tags: ["kube-logs"]
symlinks: true
json.message_key: log
json.keys_under_root: true
json.add_error_key: true