estolfo [CLIENT] Abstract logging functionality into a Loggable Module (#556)
* [CLIENT] Use Loggable module to abstract logging

* [CLIENT] Rename __log method to be more precise

* [CLIENT] Add documentation for Loggable Module

* [CLIENT] Minor spacing fix

* [CLIENT] Rollback some changes beyond the scope of this pull request
Latest commit 6b3b57e Oct 31, 2018


This library is part of the elasticsearch-ruby package; please refer to it, unless you want to use this library standalone.

The elasticsearch-transport library provides a low-level Ruby client for connecting to an Elasticsearch cluster.

It handles connecting to multiple nodes in the cluster, rotating across connections, logging and tracing requests and responses, maintaining failed connections, discovering nodes in the cluster, and provides an abstraction for data serialization and transport.

It does not handle calling the Elasticsearch API; see the elasticsearch-api library.

The library is compatible with Ruby 1.9 or higher and with all versions of Elasticsearch since 0.90.

Features overview:

  • Pluggable logging and tracing
  • Pluggable connection selection strategies (round-robin, random, custom)
  • Pluggable transport implementation, customizable and extendable
  • Pluggable serializer implementation
  • Request retries and dead connections handling
  • Node reloading (based on cluster state) on errors or on demand

For optimal performance, use a HTTP library which supports persistent ("keep-alive") connections, such as Typhoeus. Just require the library (require 'typhoeus'; require 'typhoeus/adapters/faraday') in your code, and it will be automatically used; currently these libraries will be automatically detected and used: Patron, HTTPClient and Net::HTTP::Persistent.

For detailed information, see example configurations below.


Install the package from Rubygems:

gem install elasticsearch-transport

To use an unreleased version, either add it to your Gemfile for Bundler:

gem 'elasticsearch-transport', git: 'git://'

or install it from a source code checkout:

git clone
cd elasticsearch-ruby/elasticsearch-transport
bundle install
rake install

Example Usage

In the simplest form, connect to Elasticsearch running on http://localhost:9200 without any configuration:

require 'elasticsearch/transport'

client =
response = client.perform_request 'GET', '_cluster/health'
# => #<Elasticsearch::Transport::Transport::Response:0x007fc5d506ce38 @status=200, @body={ ... } >

Full documentation is available at


The client supports many configurations options for setting up and managing connections, configuring logging, customizing the transport library, etc.

Setting Hosts

To connect to a specific Elasticsearch host: host: ''

To connect to a host with specific port: host: 'myhost:8080'

To connect to multiple hosts: hosts: ['myhost1', 'myhost2']

Instead of Strings, you can pass host information as an array of Hashes: hosts: [ { host: 'myhost1', port: 8080 }, { host: 'myhost2', port: 8080 } ]

NOTE: When specifying multiple hosts, you probably want to enable the retry_on_failure option to perform a failed request on another node (see the Retrying on Failures chapter).

Common URL parts -- scheme, HTTP authentication credentials, URL prefixes, etc -- are handled automatically: url: ''

You can pass multiple URLs separated by a comma: urls: 'http://localhost:9200,http://localhost:9201'

Another way to configure the URL(s) is to export the ELASTICSEARCH_URL variable.

The client will automatically round-robin across the hosts (unless you select or implement a different connection selector).


You can pass the authentication credentials, scheme and port in the host configuration hash: hosts: [
  { host: 'my-protected-host',
    port: '443',
    user: 'USERNAME',
    password: 'PASSWORD',
    scheme: 'https'
  } ]

... or simply use the common URL format: url: ''

To pass a custom certificate for SSL peer verification to Faraday-based clients, use the transport_options option: url: '',
                          transport_options: { ssl: { ca_file: '/path/to/cacert.pem' } }


To log requests and responses to standard output with the default logger (an instance of Ruby's {::Logger} class), set the log argument: log: true

To trace requests and responses in the Curl format, set the trace argument: trace: true

You can customize the default logger or tracer:

client.transport.logger.formatter = proc { |s, d, p, m| "#{s}: #{m}\n" }
client.transport.logger.level = Logger::INFO

Or, you can use a custom {::Logger} instance: logger:

You can pass the client any conforming logger implementation:

require 'logging' #

log = Logging.logger['elasticsearch']
log.add_appenders Logging.appenders.stdout
log.level = :info

client = logger: log

Setting Timeouts

For many operations in Elasticsearch, the default timeouts of HTTP libraries are too low. To increase the timeout, you can use the request_timeout parameter: request_timeout: 5*60

You can also use the transport_options argument documented below.

Randomizing Hosts

If you pass multiple hosts to the client, it rotates across them in a round-robin fashion, by default. When the same client would be running in multiple processes (eg. in a Ruby web server such as Thin), it might keep connecting to the same nodes "at once". To prevent this, you can randomize the hosts collection on initialization and reloading: hosts: ['localhost:9200', 'localhost:9201'], randomize_hosts: true

Retrying on Failures

When the client is initialized with multiple hosts, it makes sense to retry a failed request on a different host: hosts: ['localhost:9200', 'localhost:9201'], retry_on_failure: true

You can specify how many times should the client retry the request before it raises an exception (the default is 3 times): hosts: ['localhost:9200', 'localhost:9201'], retry_on_failure: 5

Reloading Hosts

Elasticsearch by default dynamically discovers new nodes in the cluster. You can leverage this in the client, and periodically check for new nodes to spread the load.

To retrieve and use the information from the Nodes Info API on every 10,000th request: hosts: ['localhost:9200', 'localhost:9201'], reload_connections: true

You can pass a specific number of requests after which the reloading should be performed: hosts: ['localhost:9200', 'localhost:9201'], reload_connections: 1_000

To reload connections on failures, use: hosts: ['localhost:9200', 'localhost:9201'], reload_on_failure: true

The reloading will timeout if not finished under 1 second by default. To change the setting: hosts: ['localhost:9200', 'localhost:9201'], sniffer_timeout: 3

NOTE: When using reloading hosts ("sniffing") together with authentication, just pass the scheme, user and password with the host info -- or, for more clarity, in the http options: host: 'localhost:9200',
                          http: { scheme: 'https', user: 'U', password: 'P' },
                          reload_connections: true,
                          reload_on_failure: true

Connection Selector

By default, the client will rotate the connections in a round-robin fashion, using the {Elasticsearch::Transport::Transport::Connections::Selector::RoundRobin} strategy.

You can implement your own strategy to customize the behaviour. For example, let's have a "rack aware" strategy, which will prefer the nodes with a specific attribute. Only when these would be unavailable, the strategy will use the other nodes:

class RackIdSelector
  include Elasticsearch::Transport::Transport::Connections::Selector::Base

  def select(options={}) do |c|
      # Try selecting the nodes with a `rack_id:x1` attribute first[:attributes] &&[:attributes][:rack_id] == 'x1'
    end.sample || connections.to_a.sample
end hosts: ['', ''], selector_class: RackIdSelector

Transport Implementations

By default, the client will use the Faraday HTTP library as a transport implementation.

It will auto-detect and use an adapter for Faraday based on gems loaded in your code, preferring HTTP clients with support for persistent connections.

To use the Patron HTTP, for example, just require it:

require 'patron'

Then, create a new client, and the Patron gem will be used as the "driver":

client =

# => [Faraday::Adapter::Patron]

10.times do
  client.nodes.stats(metric: 'http')['nodes'].values.each do |n|
    puts "#{n['name']} : #{n['http']['total_opened']}"

# => Stiletoo : 24
# => Stiletoo : 24
# => Stiletoo : 24
# => ...

To use a specific adapter for Faraday, pass it as the adapter argument:

client = adapter: :net_http_persistent

# => [Faraday::Adapter::NetHttpPersistent]

To pass options to the Faraday::Connection constructor, use the transport_options key:

client = transport_options: {
  request: { open_timeout: 1 },
  headers: { user_agent:   'MyApp' },
  params:  { :format => 'yaml' },
  ssl:     { verify: false }

To configure the Faraday instance directly, use a block:

require 'typhoeus'
require 'typhoeus/adapters/faraday'

client = 'localhost', port: '9200') do |f|
  f.response :logger
  f.adapter  :typhoeus

You can use any standard Faraday middleware and plugins in the configuration block, for example sign the requests for the AWS Elasticsearch service:

require 'faraday_middleware/aws_signers_v4'

client = url: '' do |f|
  f.request :aws_signers_v4,
            credentials:['AWS_ACCESS_KEY'], ENV['AWS_SECRET_ACCESS_KEY']),
            service_name: 'es',
            region: 'us-east-1'

You can also initialize the transport class yourself, and pass it to the client constructor as the transport argument:

require 'typhoeus'
require 'typhoeus/adapters/faraday'

transport_configuration = lambda do |f|
  f.response :logger
  f.adapter  :typhoeus

transport = \
  hosts: [ { host: 'localhost', port: '9200' } ],

# Pass the transport to the client
client = transport: transport

Instead of passing the transport to the constructor, you can inject it at run time:

# Set up the transport
faraday_configuration = lambda do |f|
  f.instance_variable_set :@ssl, { verify: false }
  f.adapter :excon

faraday_client = \
  hosts: [ { host: 'my-protected-host',
             port: '443',
             user: 'USERNAME',
             password: 'PASSWORD',
             scheme: 'https'

# Create a default client
client =

# Inject the transport to the client
client.transport = faraday_client

You can also use a bundled Curb based transport implementation:

require 'curb'
require 'elasticsearch/transport/transport/http/curb'

client = transport_class: Elasticsearch::Transport::Transport::HTTP::Curb

# => #<Curl::Easy http://localhost:9200/>

It's possible to customize the Curb instance by passing a block to the constructor as well (in this case, as an inline block):

transport = \
  hosts: [ { host: 'localhost', port: '9200' } ],
  & lambda { |c| c.verbose = true }

client = transport: transport

You can write your own transport implementation easily, by including the {Elasticsearch::Transport::Transport::Base} module, implementing the required contract, and passing it to the client as the transport_class parameter -- or injecting it directly.

Serializer Implementations

By default, the MultiJSON library is used as the serializer implementation, and it will pick up the "right" adapter based on gems available.

The serialization component is pluggable, though, so you can write your own by including the {Elasticsearch::Transport::Transport::Serializer::Base} module, implementing the required contract, and passing it to the client as the serializer_class or serializer parameter.

Exception Handling

The library defines a number of exception classes for various client and server errors, as well as unsuccessful HTTP responses, making it possible to rescue specific exceptions with desired granularity.

The highest-level exception is {Elasticsearch::Transport::Transport::Error} and will be raised for any generic client or server errors.

{Elasticsearch::Transport::Transport::ServerError} will be raised for server errors only.

As an example for response-specific errors, a 404 response status will raise an {Elasticsearch::Transport::Transport::Errors::NotFound} exception.

Finally, {Elasticsearch::Transport::Transport::SnifferTimeoutError} will be raised when connection reloading ("sniffing") times out.

Development and Community

For local development, clone the repository and run bundle install. See rake -T for a list of available Rake tasks for running tests, generating documentation, starting a testing cluster, etc.

Bug fixes and features must be covered by unit tests. Integration tests are written in Ruby 1.9 syntax.

Github's pull requests and issues are used to communicate, send bug reports and code contributions.

The Architecture

  • {Elasticsearch::Transport::Client} is composed of {Elasticsearch::Transport::Transport}

  • {Elasticsearch::Transport::Transport} is composed of {Elasticsearch::Transport::Transport::Connections}, and an instance of logger, tracer, serializer and sniffer.

  • Logger and tracer can be any object conforming to Ruby logging interface, ie. an instance of Logger, log4r, logging, etc.

  • The {Elasticsearch::Transport::Transport::Serializer::Base} implementations handle converting data for Elasticsearch (eg. to JSON). You can implement your own serializer.

  • {Elasticsearch::Transport::Transport::Sniffer} allows to discover nodes in the cluster and use them as connections.

  • {Elasticsearch::Transport::Transport::Connections::Collection} is composed of {Elasticsearch::Transport::Transport::Connections::Connection} instances and a selector instance.

  • {Elasticsearch::Transport::Transport::Connections::Connection} contains the connection attributes such as hostname and port, as well as the concrete persistent "session" connected to a specific node.

  • The {Elasticsearch::Transport::Transport::Connections::Selector::Base} implementations allow to choose connections from the pool, eg. in a round-robin or random fashion. You can implement your own selector strategy.


To work on the code, clone and bootstrap the main repository first -- please see instructions in the main README.

To run tests, launch a testing cluster -- again, see instructions in the main README -- and use the Rake tasks:

time rake test:unit
time rake test:integration

Unit tests have to use Ruby 1.8 compatible syntax, integration tests can use Ruby 2.x syntax and features.


This software is licensed under the Apache 2 license, quoted below.

Copyright (c) 2013 Elasticsearch <>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
See the License for the specific language governing permissions and
limitations under the License.