title: logstash cron schedule to run every 12 hours starting at certain time
body: <p>I am trying <code>0 1/12 * * *</code> cron expression but it only fires once a day. Below is 1 of my configuration.</p>
  
  <pre><code>input {
      jdbc {
          jdbc_connection_string =&gt; "jdbc:redshift://xxx.us-west-2.redshift.amazonaws.com:5439/xxx"
          jdbc_user =&gt; "xxx"
          jdbc_password =&gt; "xxx"
          jdbc_validate_connection =&gt; true
          jdbc_driver_library =&gt; "/mnt/logstash-6.0.0/RedshiftJDBC42-1.2.10.1009.jar"
          jdbc_driver_class =&gt; "com.amazon.redshift.jdbc42.Driver"
          schedule =&gt; "0 1/12 * * *" #01:00,13:00, tried from https://crontab.guru/#0_1/12_*_*_*
          statement_filepath =&gt; "conf/log_event_query.sql"
          use_column_value =&gt; true
          tracking_column =&gt; dw_insert_dt
          last_run_metadata_path =&gt; "metadata/logstash_jdbc_last_run_log_event"
      }
  }
  output {
      elasticsearch {
          index =&gt; "logs-ics_%{+dd_MM_YYYY}"
          document_type =&gt; "log_event"
          document_id =&gt; "%{log_entry_id}"
          hosts =&gt; [ "x.x.x.x:xxxx" ]
      }
  }
  </code></pre>
  
  <p>I also tried below <code>0 0 1/12 ? * * *</code> from <a href="https://www.freeformatter.com/cron-expression-generator-quartz.html" rel="nofollow noreferrer">https://www.freeformatter.com/cron-expression-generator-quartz.html</a> but lostash does not support this type.
  <a href="https://crontab.guru/#0_1/12_*_*_*" rel="nofollow noreferrer">Original</a> cron used. </p>
  
  <p>Please help me get a cron expression which works in logstash according to following dates and also is there a online page where I can test my future logstash cron expressions?</p>
  
  <pre><code>1st  at 2018-08-01 01:00:00
  then at 2018-08-01 13:00:00
  then at 2018-08-02 01:00:00
  then at 2018-08-02 13:00:00
  then at 2018-08-03 01:00:00
  </code></pre>