OpenSearch/docs/reference/modules/http.asciidoc

[[modules-http]]
=== HTTP

The HTTP layer exposes {es}'s REST 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].

[http-settings]
==== HTTP settings

The settings in the table below can be configured for HTTP. Note that none of
them are dynamically updatable so for them to take effect they should be set in
the Elasticsearch <<settings, configuration file>>.

[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`.

|`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.max_header_size` | The max size of allowed headers.  Defaults to `8kB`


|`http.compression` |Support for compression when possible (with
Accept-Encoding). If HTTPS is enabled, defaults to `false`. Otherwise, defaults
to `true`.

Disabling compression for HTTPS mitigates potential security risks, such as a
https://en.wikipedia.org/wiki/BREACH[BREACH attack]. To compress HTTPS traffic,
you must explicitly set `http.compression` to `true`.

|`http.compression_level` |Defines the compression level to use for HTTP responses. Valid values are in the range of 1 (minimum compression)
and 9 (maximum compression). Defaults to `3`.

|`http.cors.enabled` |Enable or disable cross-origin resource sharing,
i.e. whether a browser on another origin can execute requests against
Elasticsearch. Set to `true` to enable Elasticsearch to process pre-flight
https://en.wikipedia.org/wiki/Cross-origin_resource_sharing[CORS] requests.
Elasticsearch will respond to those requests with the `Access-Control-Allow-Origin` header
if the `Origin` sent in the request is permitted by the `http.cors.allow-origin`
list. Set to `false` (the default) to make Elasticsearch ignore the `Origin`
request header, effectively disabling CORS requests because Elasticsearch will
never respond with the `Access-Control-Allow-Origin` response header. Note that
if the client does not send a pre-flight request with an `Origin` header or it
does not check the response headers from the server to validate the
`Access-Control-Allow-Origin` response header, then cross-origin security is
compromised. If CORS is not enabled on Elasticsearch, the only way for the client
to know is to send a pre-flight request and realize the required response headers
are missing.

|`http.cors.allow-origin` |Which origins to allow. Defaults to no origins
allowed. 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. `*` is a valid value but is
considered a *security risk* as your Elasticsearch instance is open to cross origin
requests from *anywhere*.

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

|`http.max_warning_header_count` |The maximum number of warning headers in
 client HTTP responses, defaults to unbounded.

|`http.max_warning_header_size` |The maximum total size of warning headers in
client HTTP responses, defaults to unbounded.

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

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

[http-rest-request-tracer]
==== REST request tracer

The HTTP layer has a dedicated tracer logger which, when activated, logs incoming requests. The log can be dynamically activated
by setting the level of the `org.elasticsearch.http.HttpTracer` logger to `TRACE`:

[source,console]
--------------------------------------------------
PUT _cluster/settings
{
   "transient" : {
      "logger.org.elasticsearch.http.HttpTracer" : "TRACE"
   }
}
--------------------------------------------------

You can also control which uris will be traced, using a set of include and exclude wildcard patterns. By default every request will be
traced.

[source,console]
--------------------------------------------------
PUT _cluster/settings
{
   "transient" : {
      "http.tracer.include" : "*",
      "http.tracer.exclude" : ""
   }
}
--------------------------------------------------