How to make bash script invoking logstash return prompt

Question

For various reasons, I am not running logstash (7.10.1) as a service, but rather invoking it on-demand, in a bash script:

/usr/share/logstash/bin/logstash -f /etc/logstash/conf.d/my_ls.conf &
echo ""
echo "#########################################################"
read -p "Press enter to continue "

It works well, but when finishing to create an elasticsearch index successfully, it always pauses with:

[INFO ]  [[main]-pipeline-manager] javapipeline - Pipeline Java execution initialization time {"seconds"=>1.3}
[INFO ]  [[main]-pipeline-manager] javapipeline - Pipeline started {"pipeline.id"=>"main"}
[INFO ]  [[main]<file] observingtail - START, creating Discoverer, Watch with file and sincedb collections
[INFO ]  [Agent thread] agent - Pipelines running {:count=>1, :running_pipelines=>[:main], :non_running_pipelines=>[]}
[INFO ]  [Api Webserver] agent - Successfully started Logstash API endpoint {:port=>9600}

In order to make it return to the CLI prompt, I need to run from another SSH terminal the following:

pkill -f logstash 

This is of course inconvenient and I am looking for a way to make the bash script prompt with "Press any key to exit".

My problem is that the statements after the logstash invocation (with the & appended), including the prompt read -p "Press enter to continue" are displayed before logstash actually starts doing its work and the bash script never exits to the CLI prompt.

What is the proper way to make the bash script prompt with "Press any key to exit" when logstash finishes the index creation?

Answer 1

Solved!

Here is how:

First, it is important to acknowledge, as @roaima indicated, that it is true that logstash was not designed to build an index and then exit. Having this knowledge helps focus on a workaround as @Alex suggested. Moreover, this known limitation led to logstash-plugin based workarounds as described here:

1. exec plugin
2. exit plugin

However, a plugin requires its installation on every logstash instance and its own statement in every .conf file.

So, I found this UL answer, which spoon-fed me with the solution:

    LS_OUTPUT=$(mktemp "${TMPDIR:-/tmp/}$(basename 0).XXX")
    /usr/share/logstash/bin/logstash -f /etc/logstash/conf.d/my_ls.conf &> $LS_OUTPUT &
    LS_PID=$!

    echo "Logstash pid: ${LS_PID}"
    echo "Logstash output: $LS_OUTPUT"
    echo "Wait:"

    until grep -q -i 'agent - Successfully started Logstash API endpoint' $LS_OUTPUT
    do
      if ! ps $server_pid > /dev/null
      then
        echo "Logstash died. Exiting." >&2
        exit 1
      fi
      echo -n "."
      sleep 1
    done
    echo
    echo "Logstash is running!"