Elasticsearch::Transport

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 1.8.7 or higher and with Elasticsearch 0.90 and 1.0.

Features overview:

• Pluggable logging and tracing
• Plugabble 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, you should use a HTTP library which supports persistent ("keep-alive") connections, e.g. Typhoeus or Patron. Just require 'typhoeus' or require 'patron' in your code, and it will be used. For detailed information, see example configurations below.

Installation

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://github.com/elasticsearch/elasticsearch-ruby.git'

or install it from a source code checkout:

git clone https://github.com/elasticsearch/elasticsearch-ruby.git
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 = Elasticsearch::Client.new
response = client.perform_request 'GET', '_cluster/health'
# => #<Elasticsearch::Transport::Transport::Response:0x007fc5d506ce38 @status=200, @body={ ... } >

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

Configuration

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:

Elasticsearch::Client.new host: 'search.myserver.com'

To connect to a host with specific port:

Elasticsearch::Client.new host: 'myhost:8080'

To connect to multiple hosts:

Elasticsearch::Client.new hosts: ['myhost1', 'myhost2']

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

Elasticsearch::Client.new hosts: [ { host: 'myhost1', port: 8080 }, { host: 'myhost2', port: 8080 } ]

Elasticsearch::Client.new hosts: [
  { host: 'my-protected-host',
    port: '443',
    user: 'USERNAME',
    password: 'PASSWORD',
    scheme: 'https'
  } ]

Scheme, HTTP authentication credentials and URL prefixes are handled automatically:

Elasticsearch::Client.new url: 'https://username:password@api.server.org:4430/search'

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

Logging

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

Elasticsearch::Client.new log: true

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

Elasticsearch::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:

Elasticsearch::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 = Elasticsearch::Client.new logger: log

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:

Elasticsearch::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:

Elasticsearch::Client.new 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:

Elasticsearch::Client.new 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:

Elasticsearch::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:

Elasticsearch::Client.new hosts: ['localhost:9200', 'localhost:9201'], reload_connections: 1_000

To reload connections on failures, use:

Elasticsearch::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:

Elasticsearch::Client.new hosts: ['localhost:9200', 'localhost:9201'], sniffer_timeout: 3

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={})
    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
  end
end

Elasticsearch::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 = Elasticsearch::Client.new

client.transport.connections.first.connection.builder.handlers
# => [Faraday::Adapter::Patron]

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

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

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

client = Elasticsearch::Client.new adapter: :net_http_persistent

client.transport.connections.first.connection.builder.handlers
# => [Faraday::Adapter::NetHttpPersistent]

To configure the Faraday instance, pass a configuration block to the transport constructor:

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

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

transport = Elasticsearch::Transport::Transport::HTTP::Faraday.new \
  hosts: [ { host: 'localhost', port: '9200' } ],
  &transport_configuration

# Pass the transport to the client
#
client = Elasticsearch::Client.new transport: transport

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

client = Elasticsearch::Client.new transport_options: {
  request: { open_timeout: 1 },
  headers: { user_agent:   'MyApp' },
  params:  { :format => 'yaml' }
}

You can also use a bundled Curb based transport implementation:

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

client = Elasticsearch::Client.new transport_class: Elasticsearch::Transport::Transport::HTTP::Curb

client.transport.connections.first.connection
# => #<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 = Elasticsearch::Transport::Transport::HTTP::Curb.new \
  hosts: [ { host: 'localhost', port: '9200' } ],
  & lambda { |c| c.verbose = true }

client = Elasticsearch::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
end

faraday_client = Elasticsearch::Transport::Transport::HTTP::Faraday.new \
  hosts: [ { host: 'my-protected-host',
             port: '443',
             user: 'USERNAME',
             password: 'PASSWORD',
             scheme: 'https'
          }],
  &faraday_configuration

# Create a default client
#
client = Elasticsearch::Client.new

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

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.

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.

License

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

Copyright (c) 2013 Elasticsearch <http://www.elasticsearch.org>

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

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

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