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Introduction to Elasticsearch

If you've found yourself on this page, you're most likely taking my basic introduction to Elasticsearch course and are trying to follow along. The resources in this project are nothing more than the minimal set of files and queries needed to walk through the "Chat log analysis" case study of Elasticsearch which, for ease of use, I'll provide a brief review of here.

Case Study: Chat Log Analysis

Given a dump of slack logs, I'd like to be able to answer the following questions:

  • Which user are most commonly posting GIFs?
  • What have people saying about me?
  • How does chat activity vary over time?

Getting Started

Prerequisites

To follow along with this guide, you will need the following tools installed and available on your local machine:

  • A terminal w/ basic command-line skills
  • A running Elasticsearch node (or access to one)

1. Clone this project

To get started, you'll first need to clone this project:

cd /path/to/your/workspace
git clone https://github.com/rusnyder/intro-to-es

2. Start up your Elasticsearch node

This guide assumes that you either already have an Elasticsearch node running and accessible or that you are able to create one without guidance.

NOTE: All commands from this point assume your Elasticsearch node has its HTTP service available at the location http://localhost:9200

3. Create an index template for all our indices

To make sure that our indexed data gets analyzed the way we want, we need to make sure that we give Elasticsearch the appropriate settings/mappings for our data prior to indexing any data. This can be done in two ways:

  1. Create all our indices with the settings/mappings
  2. Create an index template that will apply settings/mappings as any new indices get created

For simplicity, we COULD go with option #1, but for the sake of completeness and "best practices", this example will walk through #2.

Creating our Template

This project provides a template that matches on any indices named intro-to-es-* (note the wildcard), which means that any index created with a matching name will get created with all of the settings and mappings from that template. This is nice because once the template has been created, we can just start indexing data and new indices will automatically pick up their appropriate settings.

Let's go ahead and upload the template (using intro-to-es-template.json):

curl -XPUT http://localhost:9200/_template/intro-to-es -d @intro-to-es-template.json

4. Index some data

This project provides some sample data in the file bulk-index.jsonl that are already in a format the Elasticsearch's Bulk API accepts, so indexing our data is as simple as POSTing that file to Elasticsearch:

# Delete any data from a previous run of these steps
curl -XDELETE 'http://localhost:9200/intro-to-es*'

# Index our events using the bulk API and refreshing
# to make them available for search immediately
curl -XPOST http://localhost:9200/_bulk --data-binary @bulk-index.jsonl

# Run a quick count just to see that your documents were
# indexed and that the "intro-to-es" alias was created
curl http://localhost:9200/intro-to-es/_count

NOTE: cURL will strip newlines from any data provided using the -d/--data option, so we must use the --data-binary option to preserve the newlines which are necessary for proper interpretation of the bulk request body.

5. Now we're ready for some queries!

At this point, we've got our data indexed and are ready to start answering some questions!

Question 1: Which users are most commonly posting GIFs?

Here we just want to find the top senders using the /gif slack directive, and since our analyzer only preserves slashes when they are at the beginning of the sentence, we know that if we match the token /gif, then it's the directive that we're looking for and not just the string "/gif" occurring in the middle of a sentence.

Once we subset the events, aggregating over from gives us the top senders.

POST /intro-to-es/_search
{
  "query": {
    "term": {
      "message": "/gif"
    }
  },
  "aggs": {
    "top_senders": {
      "terms": {
        "field": "from",
        "size": 0
      }
    }
  }
}

Question 2: What have people saying about me?

To answer this, we want to take a look at the chat messages that are most relevant, with "relevance" here loosely being defined as "how likely is it that this message pertains to or is about me?". For this, we use a couple of clauses with boost factors as a means of saying occurrences of certain tokens/phrases can be treated as "more certainly me" than others.

POST /intro-to-es/_search
{
  "query": {
    "bool": {
      "should": [
        {
          "term": {
            "message": {
              "value": "@rusnyder",
              "boost": 10
            }
          }
        },
        {
          "match": {
            "message": {
              "query": "russell,snyder",
              "boost": 2
            }
          }
        },
        {
          "prefix": {
            "message": {
              "value": "russ",
              "boost": 1
            }
          }
        }
      ]
    }
  }
}