[[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].

[float]
=== 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.publish_port` |The port that HTTP clients should use when
communicating with this node. Useful when a cluster node is behind a
proxy or firewall and the `http.port` is not directly addressable
from the outside. Defaults to the actual port assigned via `http.port`.

|`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.detailed_errors.enabled` |Enables or disables the output of detailed error messages
and stack traces in response output. Note: When set to `false` and the `error_trace` request
parameter is specified, an error will be returned; when `error_trace` is not specified, a
simple message will be returned. Defaults to `true`

|`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>>.

[float]
=== Disable HTTP

The http module can be completely disabled and not started by setting
`http.enabled` to `false`. Elasticsearch nodes (and Java clients) communicate
internally using the <<modules-transport,transport interface>>, not HTTP. It
might make  sense to disable the `http` layer entirely on nodes which are not
meant to serve REST requests directly. For instance, you could disable HTTP on
<<modules-node,data-only nodes>> if you also have
<<modules-node,client nodes>> which are intended to serve all REST requests.
Be aware, however, that you will not be able to send any REST requests (eg to
retrieve node stats) directly to nodes which have HTTP disabled.