JSON Filter Making Events Disappear

I've been using the same filter configuration across multiple upgrades of Logstash. After upgrading to 7.10.0, the JSON filter now makes events...disappear. Events are sent to Logstash via filebeat (running v 7.10.0). I've tested my configs and events get ingested into Elasticsearch up to the point that I use the JSON filter. Logstash and Elasticsearch logs don't show any errors. I'm using a very barebones implementation

json {
  source => "temp_message"

Example data in the temp_message field

{"action": "post /validate/check", "action_detail": "", "client": "", "client_user_agent": null, "info": "err905: missing parameter: 'pass'", "policies": "", "server": "example", "success": false, "timestamp": "2020-11-20t22:49:40.110520"}

How can I track down what the hell is going on?

I would start by enabling log.level debug and verifying that you see events going in and out of the filter.

It was terrible, but I have verified with debug enabled that events are coming into Logstash

And you see the messages from both of these for each event?

@logger.debug("Running json filter", :event => event)

@logger.debug("Event after json filter", :event => event)

Actually no....I have five pipelines running with multiple instances of json being called and I don't have any events like that. Searching the logs for logstash.filters.json turns up nothing. What I see is


The reason I assumed this is the JSON filter is based on the event content. I wonder if the json plugin didn't update or something...

Alright, I've done some more research on this. This is my only beats input pipeline and within this pipeline, I split off and parse seven different log sources. They all end up in a variety of indices in Elasticsearch with a catch-all index at the end. The JSON filter is only called the one time in this pipeline. With filter debugging enabled (as defined here) and pipeline.log_sources: true set in my logstash.yml. The below gets logged in the beats pipeline log.

[DEBUG][logstash.filters.json    ] Running json filter {:event=>#<LogStash::Event:0xb7d5666>}
[DEBUG][logstash.filters.json    ] Event after json filter {:event=>#<LogStash::Event:0x293d386d>}

The below gets logged in logstash-plain.log

[2020-11-25T09:33:05,914][DEBUG][logstash.filters.json    ] config LogStash::Filters::Json/@source = "privacyidea_message"
[2020-11-25T09:33:06,227][DEBUG][logstash.filters.json    ] config LogStash::Filters::Json/@id = "fbfef07ebe7f412de7b8b68d807e971d25b17c19168877ebfa99ff36e17b788e"
[2020-11-25T09:33:06,367][DEBUG][logstash.filters.json    ] config LogStash::Filters::Json/@enable_metric = true
[2020-11-25T09:33:06,388][DEBUG][logstash.filters.json    ] config LogStash::Filters::Json/@add_tag = []
[2020-11-25T09:33:06,423][DEBUG][logstash.filters.json    ] config LogStash::Filters::Json/@remove_tag = []
[2020-11-25T09:33:06,453][DEBUG][logstash.filters.json    ] config LogStash::Filters::Json/@add_field = {}
[2020-11-25T09:33:06,492][DEBUG][logstash.filters.json    ] config LogStash::Filters::Json/@remove_field = []
[2020-11-25T09:33:06,529][DEBUG][logstash.filters.json    ] config LogStash::Filters::Json/@periodic_flush = false
[2020-11-25T09:33:06,537][DEBUG][logstash.filters.json    ] config LogStash::Filters::Json/@tag_on_failure = ["_jsonparsefailure"]
[2020-11-25T09:33:06,537][DEBUG][logstash.filters.json    ] config LogStash::Filters::Json/@skip_on_invalid_json = false

Pipeline Configuration - Removed parts of pipeline that do not effect these logs. (Full pipe is like 700 lines)

input {
  beats {
    id => "Beats Input"
    port => 5044
    include_codec_tag => false
filter {
  else if [@metadata][beat] == "filebeat" {
    if [log][source] == "privacyidea" {
      fingerprint {
        id => "PrivacyIDEA Duplication Protection"
        source => "message"
        target => "[@metadata][fingerprint]"
        method => "MURMUR3"
      #Drop java errors
      if [message] =~ /^(Traceback|KeyError|\s)/ {
        drop { }
      #JSON non-JSON formatted messages
      if [message] =~ /^\[.*?\]\[.*?\]\[.*?\]\w.*/ {
        mutate {
          id => "PrivacyIDEA JSON Encode messages"
          gsub => [
            "message", '(\[.*?\]\[.*?\]\[.*?\])(.*)', '\1{"info": "\2"}'
      #Normalize message
      mutate {
        id => "PrivacyIDEA lowercase message"
        lowercase => [ "message" ]
      #Parse syslog formatted fields out
      grok {
        id => "PrivacyIDEA syslog parsing"
        match => ["message", "\[%{TIMESTAMP_ISO8601:time}]\[%{LOGLEVEL:log_level}]\[%{SYSLOGPROG:module}]%{GREEDYDATA:privacyidea_message}"]
      json {
        source => "privacyidea_message"
output {
  else if [@metadata][beat] == "filebeat" {
    if [log][source] == "privacyidea" {
      elasticsearch {
        id => "PrivacyIDEA Output"
        hosts => "ElasticsearchServer:9200"
        document_id => "%{[@metadata][fingerprint]}"
        index => "privacyidea-%{+YYYY.MM}"
    else {
      elasticsearch {
        id => "Filebeat Out"
        cacert => "D:/Logstash/config/certs/realbundle.pem"
        user => "elastic"
        password => "K6m^OsUUoE&E"
        hosts => "https://ssselklog.stlouisco.net:9200"
        ilm_rollover_alias => "filebeat"
        ilm_pattern => "{now/d}-000001"
        ilm_policy => "Delete_After_30D"
        template => "D:/Logstash/templates/filebeattemplate.json"
        template_name => "filebeat"
        template_overwrite => true

Removing the json filter from my pipeline, the below event gets ingested into elasticsearch. I included a couple different fields to

message field

[2020-11-25 09:32:58,952][info][pi-audit]{"action": "post /validate/check", "action_detail": "", "client": "", "client_user_agent": null, "info": "err905: missing parameter: 'pass'", "policies": "", "privacyidea_server": "contoso", "success": false, "timestamp": "2020-11-25t15:32:58.952025"}

privacyidea_message field

{"action": "post /validate/check", "action_detail": "", "client": "", "client_user_agent": null, "info": "err905: missing parameter: 'pass'", "policies": "", "privacyidea_server": "contoso", "success": false, "timestamp": "2020-11-25t15:32:58.952025"}

_source field

agent.id:369a6767-44ee-4bc3-abd9-cd168e3e9849 agent.version:7.10.0 agent.ephemeral_id:7ce8f4f1-5d97-4295-bec3-e97bf2f629f4 agent.hostname:contoso agent.type:filebeat agent.name:contoso message:[2020-11-25 09:32:58,952][info][pi-audit]{"action": "post /validate/check", "action_detail": "", "client": "", "client_user_agent": null, "info": "err905: missing parameter: 'pass'", "policies": "", "privacyidea_server": "contoso", "success": false, "timestamp": "2020-11-25t15:32:58.952025"} log_level:info ecs.version:1.6.0 host.name:contoso log.source:privacyidea log.file.path:/var/log/privacyidea/audit.log log.offset:20269333 module:pi-audit @version:1 privacyidea_message:{"action": "post /validate/check", "action_detail": "", "client": "", "client_user_agent": null, "info": "err905: missing parameter: 'pass'", "policies": "", "privacyidea_server": "contoso", "success": false, "timestamp": "2020-11-25t15:32:58.952025"} program:pi-audit time:2020-11-25 09:32:58,952 input.type:log @timestamp:Nov 25, 2020 @ 09:32:59.262 _id:557983225 _index:privacyidea-2020.11

It is odd that the address of the event returned by the json filter is not the same as the address of the event passed to it. The json filter modifies the event, it does not replace it.

I cannot see anything that would stop the event being indexed. The only thing I can think of is that parsing the JSON adds a field that you are testing in a conditional, resulting in the event either being dropped, or going to an output that you do not expect.

That's my fault, I just grabbed the two entries next to eachother. Searching the logs, there is an open and a close with the same event address.

I stumbled onto something interesting and a solution. Looking at the pipeline in Kibana Monitoring, I saw that events were being processed by each step of the pipeline AND by the output to Elasticsearch. It didn't dawn on me to check the Elasticsearch logs immediately, so I changed the index in the elasticsearch output and I started seeing events again.

So I looked at elasticsearch logs and, though I'm not sure why, it appears that the filtering changed the structure of the output and elasticsearch was failing to ingest documents because it was expecting an object and not a concrete value for a certain field.

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