Log events not stored in syslog persistent queue

We are using Logstash 8.3.0. We are using syslog output with persistent queue. Please see following configuration.

http.host: ""
http.port: 9600
log.level: "info"
pipeline.workers: 2
pipeline.batch.size: 2048
pipeline.batch.delay: 50
path.logs: /opt/logstash/resource
pipeline.ecs_compatibility: disabled

- pipeline.id: logstash
  queue.type: persisted
  queue.max_bytes: 1024mb
  path.config: "/opt/logstash/config/logstash.conf"
- pipeline.id: opensearch
  queue.type: persisted
  queue.max_bytes: 1024mb
  path.config: "/opt/logstash/config/searchengine.conf"
- pipeline.id: syslog
  queue.type: persisted
  queue.max_bytes: 1024mb
  path.config: "/opt/logstash/config/syslog_output.conf"


input { pipeline { address => "syslog_pipeline" } }

 filter {
   if [facility] == "log audit"
   or [facility] == "security/authorization messages"
   or "-privacy-" in [metadata][category]
       if [extra_data][asi][log_plane] == "alarm" {
   else {
 output {
   syslog {
     host => "rsyslog"
     port => 514
     protocol => tcp
     rfc => rfc5424
     use_labels => false
     appname => "%{appname}"
     priority => "%{priority}"
     message => "%{message}"
     sourcehost => "%{sourcehost}"
     procid => "%{[metadata][proc_id]}"
     msgid => "%{[metadata][category]}"

When the syslog sever is down, the log events are not getting stored in the syslog persistent queue. Could you please check and suggest.

OpenSearch/OpenDistro are AWS run products and differ from the original Elasticsearch and Kibana products that Elastic builds and maintains. You may need to contact them directly for further assistance.

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What do you have in Logstash logs? Please share any log that indicates that.

Also, did you check the size of the queue path? Your queue should store the events until it is full, in your case you set it to a maximum 1 GB.

We do not see any logs in the logstash logs during the issue.

Normally, when syslog server is down, logstash will keep trying to connect to syslog server and we see following log in logstash.

{"version": "1.1.0", "timestamp": "2023-01-10T06:03:17.823Z", "severity": "warning", "service_id": "eric-log-transformer", "metadata" : {"namespace": "xferdsh", "pod_name": "eric-log-transformer-75c84c8864-fbd8z", "container_name": "logtransformer"}, "message": "[logstash.outputs.syslog] syslog tcp output exception: closing, reconnecting and resending event {:host=>'rsyslog', :port=>514, :exception=>#<SocketError: initialize: name or service not known>,

But, in this case we do not see such errors.

The pipeline statistics shows, there is enough free space in the syslog queue and stored events count shows as 0.

    "syslog" : {
          "path" : "/opt/logstash/data/queue/syslog",
          "storage_type" : "ext4"
        "events_count" : 0,
        "queue_size_in_bytes" : 4929,
        "max_queue_size_in_bytes" : 1073741824

When we try to send more log events (i.e more than 5000 log events), we see some log events are getting stored in the queue. But when we try with less log events (i.e less than 2000 log events), logs are not stored in the queue.

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