[[modules-http]]
== HTTP

The http module allows to expose *elasticsearch* APIs
over HTTP.

The http mechanism is completely asynchronous in nature, meaning that
there is no blocking thread waiting for a response. The benefit of using
asynchronous communication for HTTP is solving the
http://en.wikipedia.org/wiki/C10k_problem[C10k problem].

When possible, consider using
http://en.wikipedia.org/wiki/Keepalive#HTTP_Keepalive[HTTP keep alive]
when connecting for better performance and try to get your favorite
client not to do
http://en.wikipedia.org/wiki/Chunked_transfer_encoding[HTTP chunking].

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=== Settings

The following are the settings that can be configured for HTTP:

[cols="<,<",options="header",]
|=======================================================================
|Setting |Description
|`http.port` |A bind port range. Defaults to `9200-9300`.

|`http.bind_host` |The host address to bind the HTTP service to. Defaults to `http.host` (if set) or `network.bind_host`.

|`http.publish_host` |The host address to publish for HTTP clients to connect to. Defaults to `http.host` (if set) or `network.publish_host`.

|`http.host` |Used to set the `http.bind_host` and the `http.publish_host` Defaults to `http.host` or `network.host`.

|`http.max_content_length` |The max content of an HTTP request. Defaults
to `100mb`

|`http.max_initial_line_length` |The max length of an HTTP URL. Defaults
to `4kb`

|`http.compression` |Support for compression when possible (with
Accept-Encoding). Defaults to `false`.

|`http.compression_level` |Defines the compression level to use.
Defaults to `6`.

|`http.cors.enabled` |Enable or disable cross-origin resource sharing,
i.e. whether a browser on another origin can do requests to
Elasticsearch. Defaults to `false`.

|`http.cors.allow-origin` |Which origins to allow. Defaults to `*`,
i.e. any origin. If you prepend and append a `/` to the value, this will
be treated as a regular expression, allowing you to support HTTP and HTTPs.
for example using `/https?:\/\/localhost(:[0-9]+)?/` would return the
request header appropriately in both cases.

|`http.cors.max-age` |Browsers send a "preflight" OPTIONS-request to
determine CORS settings. `max-age` defines how long the result should
be cached for. Defaults to `1728000` (20 days)

|`http.cors.allow-methods` |Which methods to allow. Defaults to
`OPTIONS, HEAD, GET, POST, PUT, DELETE`.

|`http.cors.allow-headers` |Which headers to allow. Defaults to
`X-Requested-With, Content-Type, Content-Length`.

|`http.cors.allow-credentials` | Whether the `Access-Control-Allow-Credentials`
header should be returned. Note: This header is only returned, when the setting is
set to `true`. Defaults to `false`

|`http.pipelining` |Enable or disable HTTP pipelining, defaults to `true`.

|`http.pipelining.max_events` |The maximum number of events to be queued up in memory before a HTTP connection is closed, defaults to `10000`.

|=======================================================================

It also uses the common
<<modules-network,network settings>>.

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=== Disable HTTP

The http module can be completely disabled and not started by setting
`http.enabled` to `false`. This make sense when creating non
<<modules-node,data nodes>> which accept HTTP
requests, and communicate with data nodes using the internal
<<modules-transport,transport>>.