Using Nifi to convert CSV to JSON and store in Elasticsearch

In this post I’ll share a Nifi workflow that takes in CSV files, converts them to JSON, and stores them in different Elasticsearch indexes based on the file schema. I created a JRuby ExecuteScript processor to use the header row of the CSV file as the JSON schema, and the filename to determine which index/type to use for each Elasticsearch document.

For this post I used homebrew on OSX, but you could use Docker, install from source, etc.

Example install:

# ex: install/start elasticsearch
brew install elasticsearch
brew services start elasticsearch
# browse to http://localhost:9200

# ex: install/start nifi
brew install nifi
export NIFI_HOME="/usr/local/Cellar/nifi/1.5.0/libexec"
$NIFI_HOME/bin/nifi start
# browse to http://localhost:8080/nifi/

My planned Nifi workflow:

  • Get a list of CSV files from a local directory
  • ExecuteScript processor to convert them to JSON, use the header row as the JSON schema, and set index/type attribute on each flow file
  • SplitJson processor to convert JSON array of objects to individual JSON records
  • PutElasticsearch processor to send to Elasticsearch, routed to index/type based on flow file attribute

Screenshot of workflow: Nifi CSV to JSON workflow

1. GetFile

  • Input directory: /nifi/in/
  • File filter: [^\.].*\.csv$

2. ExecuteScript

  • Script engine: ruby
  • Script file: /nifi/scripts/csv_to_json.rb

Contents of /nifi/scripts/csv_to_json.rb:

java_import java.nio.charset.StandardCharsets

require 'csv'
require 'fileutils'
require 'json'
require 'logger'

class FileStreamCallback
  include StreamCallback

  def process(in_stream, out_stream)
    # read file as text
    text = IOUtils.toString(in_stream, StandardCharsets::UTF_8)

    # parse CSV, convert to JSON using header row
    csv_data = CSV.parse(text)
    header_row = csv_data.shift
    json_data = {|row| Hash[] }
    json_string = json_data.to_json

    # rewrite file as json string

flowfile = session.get()
if flowfile.nil?

# setup logger
log_path = '/nifi/logs/'
log_file = 'csv_to_json.log'
FileUtils.mkdir_p(log_path) unless
$logger ="#{log_path}#{log_file}")

# ensure we only process csv files (note: this is redundant)
filename = flowfile.getAttribute('filename')
if filename !~ /\.csv$/
  $logger.warn("File extension must be csv: #{filename}")
  session.transfer(flowfile, REL_FAILURE)


  # create a new StreamCallback instance and write to flow file
  stream_callback =
  flowfile = session.write(flowfile, stream_callback)

  # update filename extension
  new_filename = filename.gsub(/\.csv$/, '.json')
  flowfile = session.putAttribute(flowfile, 'filename', new_filename)

  # set index/type
  index_type = /^(.*)\.json$/.match(new_filename)[1].downcase
  index_type = /^(.*?)_part/.match(index_type)[1] if index_type =~ /_part/
  flowfile = session.putAttribute(flowfile, 'index_type', index_type)

  $"file: #{filename}; new file: #{new_filename}; index_type: #{index_type}")
  session.transfer(flowfile, REL_SUCCESS)

rescue => e

  session.transfer(flowfile, REL_FAILURE)


3. SplitJson

  • Converts JSON array of objects to individual objects
  • JsonPath Expression: $.*

4. PutElasticsearch

  • Cluster name: elasticsearch
  • ElasticSearch Hosts: localhost:9300
  • Identifier Attribute: uuid
  • Index: ${index_type}
  • Type: ${index_type}

Note: cluster name must match Elasticsearch server configuration, ex:

grep -i /usr/local/etc/elasticsearch/elasticsearch.yml elasticsearch

5. PutFile

  • Used for failure connections
  • Directory: /nifi/errors/
  • Conflict Resolution Strategy: replace
  • Create Missing Directories: true

I create some scripts to generate data, ex:

#!/usr/bin/env ruby

require 'csv'
require 'faker'

file_counter = 0
csv_data = []

people = (1..PEOPLE_COUNT).map do |id|
  if csv_data.size == 0
    csv_data << %w(id first_name last_name email)

  csv_data << [

  # note: this does not check last iteration
  if csv_data.size > ROWS_PER_FILE
    file_counter += 1
    file_name = "people_part_#{file_counter}.csv""./#{file_name}", "wb") do |csv|
      csv_data.each do |c|
        csv << c
    csv_data = []

I executed the data creation scripts, and then copied the CSV files into the input directory, ex: cp /nifi/data/*.csv /nifi/in/

Contents of the ExecuteScript log file:

tail -f /nifi/logs/csv_to_json.log
I, [2018-03-04T10:23:28.763877 #75354]  INFO -- : file: people_part_2.csv; new file: people_part_2.json; index_type: people
I, [2018-03-04T10:23:28.779399 #75354]  INFO -- : file: people_part_13.csv; new file: people_part_13.json; index_type: people
I, [2018-03-04T10:23:28.797090 #75354]  INFO -- : file: products_part_15.csv; new file: products_part_15.json; index_type: products
I, [2018-03-04T10:23:28.805136 #75354]  INFO -- : file: products_part_4.csv; new file: products_part_4.json; index_type: products
I, [2018-03-04T10:23:28.822709 #75354]  INFO -- : file: products_part_9.csv; new file: products_part_9.json; index_type: products
I, [2018-03-04T10:23:28.832498 #75354]  INFO -- : file: products_part_10.csv; new file: products_part_10.json; index_type: products
I, [2018-03-04T10:23:28.855308 #75354]  INFO -- : file: people_part_12.csv; new file: people_part_12.json; index_type: people
I, [2018-03-04T10:23:28.870675 #75354]  INFO -- : file: people_part_20.csv; new file: people_part_20.json; index_type: people
I, [2018-03-04T10:23:28.879414 #75354]  INFO -- : file: people_part_4.csv; new file: people_part_4.json; index_type: people
I, [2018-03-04T10:23:28.887039 #75354]  INFO -- : file: products_part_8.csv; new file: products_part_8.json; index_type: products

Inspecting data in Elasticsearch:

curl 'http://localhost:9200/people/_search?pretty&size=1'
  "took" : 4,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "failed" : 0
  "hits" : {
    "total" : 1000,
    "max_score" : 1.0,
    "hits" : [ {
      "_index" : "people",
      "_type" : "people",
      "_id" : "d49a4a19-48ed-47c5-b855-a18f798d0ce0",
      "_score" : 1.0,
      "_source" : {
        "id" : "8",
        "first_name" : "Eric",
        "last_name" : "London",
        "email" : ""
    } ]

Source code on Github