Elastic Transport

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This gem provides a low-level Ruby client for connecting to an Elastic cluster. It powers both the Elasticsearch client and the Elastic Enterprise Search client.


This gem is compatible with maintained Ruby versions. See Ruby Maintenance Branches. We don't provide support to versions which have reached their end of life.


Install the package from Rubygems:

gem install elastic-transport

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

gem 'elastic-transport', git: 'git://github.com/elastic/elastic-transport-ruby.git'

or install it from a source code checkout:

git clone https://github.com/elastic/elastic-transport-ruby.git
cd elastic-transport-ruby
bundle install
rake install


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 library for that.

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 patron or Typhoeus. Just require the library (require 'patron') in your code, and it will be automatically used.

Currently these libraries will be automatically detected and used:

Note on Typhoeus: You need to use v1.4.0 or up since older versions are not compatible with Faraday 1.0.

For detailed information, see example configurations below.

Example Usage

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

require 'elastic/transport'

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

Full documentation is available at http://rubydoc.info/gems/elastic-transport.


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

Setting Hosts

This behaviour is going to be simplified, see #5. To connect to a specific Elasticsearch host:

Elastic::Transport::Client.new(host: 'search.myserver.com')

To connect to a host with specific port:

Elastic::Transport::Client.new(host: 'myhost:8080')

To connect to multiple hosts:

Elastic::Transport::Client.new(hosts: ['myhost1', 'myhost2'])

Instead of Strings, you can pass host information as an array of Hashes:

Elastic::Transport::Client.new(hosts: [{ host: 'myhost1', port: 8080 }, { host: 'myhost2', port: 8080 }])

NOTE: When specifying multiple hosts, you probably want to enable the retry_on_failure or retry_on_status options 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:

Elastic::Transport::Client.new(url: 'https://username:[email protected]:4430/search')

You can pass multiple URLs separated by a comma:

Elastic::Transport::Client.new(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).

Default port

The default port is 9200. Please specify a port for your host(s) if they differ from this default. Please see below for an exception to this when connecting using an Elastic Cloud ID.


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 use the common URL format:

Elastic::Transport::Client.new(url: 'https://username:[email protected]:9200')

To pass a custom certificate for SSL peer verification to Faraday-based clients, use the transport_options option:

  url: 'https://username:[email protected]:9200',
  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 to true:

Elastic::Transport::Client.new(log: true)

You can also use ecs-logging. ecs-logging is a set of libraries that allows you to transform your application logs to structured logs that comply with the Elastic Common Schema (ECS):

logger = EcsLogging::Logger.new($stdout)
Elastic::Transport::Client.new(logger: logger)

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

Elastic::Transport::Client.new(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:

Elastic::Transport::Client.new(logger: Logger.new(STDERR))

You can pass the client any conforming logger implementation:

require 'logging' # https://github.com/TwP/logging/

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

client = Elastic::Transport::Client.new(logger: log)

Custom HTTP Headers

You can set a custom HTTP header on the client's initializer:

client = Elastic::Transport::Client.new(
  transport_options: {
      {user_agent: "My App"}

You can also pass in headers as a parameter to any of the API Endpoints to set custom headers for the request:

client.search(index: 'myindex', q: 'title:test', headers: { user_agent: "My App" })

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:

Elastic::Transport::Client.new(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:

Elastic::Transport::Client.new(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:

Elastic::Transport::Client.new(hosts: ['localhost:9200', 'localhost:9201'], retry_on_failure: true)

By default, the client will retry the request 3 times. You can specify how many times to retry before it raises an exception by passing a number to retry_on_failure:

Elastic::Transport::Client.new(hosts: ['localhost:9200', 'localhost:9201'], retry_on_failure: 5)

You can also use retry_on_status to retry when specific status codes are returned:

Elastic::Transport::Client.new(hosts: ['localhost:9200', 'localhost:9201'], retry_on_status: [502, 503])

These two parameters can also be used together:

Elastic::Transport::Client.new(hosts: ['localhost:9200', 'localhost:9201'], retry_on_status: [502, 503], retry_on_failure: 10)

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:

Elastic::Transport::Client.new(hosts: ['localhost:9200', 'localhost:9201'], reload_connections: true)

You can pass a specific number of requests after which the reloading should be performed:

Elastic::Transport::Client.new(hosts: ['localhost:9200', 'localhost:9201'], reload_connections: 1_000)

To reload connections on failures, use:

Elastic::Transport::Client.new(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:

Elastic::Transport::Client.new(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 Elastic::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 Elastic::Transport::Transport::Connections::Selector::Base

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

Elastic::Transport::Client.new hosts: ['x1.search.org', 'x2.search.org'], 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 = Elastic::Transport::Client.new

# => 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 = Elastic::Transport::Client.new(adapter: :net_http_persistent)

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

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

client = Elastic::Transport::Client.new(
  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 'patron'

client = Elastic::Transport::Client.new(host: 'localhost', port: '9200') do |f|
  f.response :logger
  f.adapter  :patron

You can use any standard Faraday middleware and plugins in the configuration block. You can also initialize the transport class yourself, and pass it to the client constructor as the transport argument:

require 'patron'

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

transport = Elastic::Transport::Transport::HTTP::Faraday.new(
  hosts: [ { host: 'localhost', port: '9200' } ],

# Pass the transport to the client
client = Elastic::Transport::Client.new(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 = Elastic::Transport::Transport::HTTP::Faraday.new(
  hosts: [
      host: 'my-protected-host',
      port: '443',
      user: 'USERNAME',
      password: 'PASSWORD',
      scheme: 'https'

# Create a default client
client = Elastic::Transport::Client.new

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

You can also use a bundled Curb based transport implementation:

require 'curb'
require 'elastic/transport/transport/http/curb'

client = Elastic::Transport::Client.new(transport_class: Elastic::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 = Elastic::Transport::Transport::HTTP::Curb.new(
  hosts: [ { host: 'localhost', port: '9200' } ],
  & lambda { |c| c.verbose = true }

client = Elastic::Transport::Client.new(transport: transport)

You can write your own transport implementation by including the Elastic::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 Elastic::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 Elastic::Transport::Transport::Error and will be raised for any generic client or server errors.

Elastic::Transport::Transport::ServerError will be raised for server errors only.

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

Finally, Elastic::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.

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

The Architecture

  • Elastic::Transport::Client is composed of Elastic::Transport::Transport.
  • Elastic::Transport::Transport is composed of Elastic::Transport::Transport::Connections, and an instance of logger, tracer, serializer and sniffer.
  • Logger and tracer can be any object conforming to the Ruby logging interface, ie. an instance of Logger, log4r, logging, etc.
  • The Elastic::Transport::Transport::Serializer::Base implementations handles converting data for Elasticsearch (eg. to JSON). You can implement your own serializer.
  • Elastic::Transport::Transport::Sniffer allows discovering nodes in the cluster and use them as connections.
  • Elastic::Transport::Transport::Connections::Collection is composed of Elastic::Transport::Transport::Connections::Connection instances and a selector instance.
  • Elastic::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 Elastic::Transport::Transport::Connections::Selector::Base implementations allows you to choose connections from the pool, eg. in a round-robin or random fashion. You can implement your own selector strategy.


A rake task is included to launch an Elasticsearch cluster with Docker. You need to install docker on your system and then run:

$ rake docker:start[VERSION]


$ rake docker:start[8.0.0-alpha1]

You can find the available version in Docker @ Elastic.

To run tests, launch a testing cluster and use the Rake tasks:

time rake test:unit
time rake test:integration

Use COVERAGE=true before running a test task to check coverage with Simplecov.


This software is licensed under the Apache 2 license.