3.5. CouchDB HTTP Server — Apache CouchDB® 3.2 Documentation

# 3.5. CouchDB HTTP Server

## 3.5.1. HTTP Server Options

`[chttpd]`

  Note

  In CouchDB 2.x and 3.x, the chttpd section refers to the standard, clustered port. All use of CouchDB, aside from a few specific maintenance tasks as described in this documentation, should be performed over this port.

  `bind_address`

    Defines the IP address by which the clustered port is available:

        [chttpd]
        bind_address = 127.0.0.1

    To let CouchDB listen any available IP address, use `0.0.0.0`:

        [chttpd]
        bind_address = 0.0.0.0

    For IPv6 support you need to set `::1` if you want to let CouchDB listen correctly:

        [chttpd]
        bind_address = ::1

    or `::` for any available:

        [chttpd]
        bind_address = ::

  `port`

    Defines the port number to listen:

        [chttpd]
        port = 5984

    To let CouchDB use any free port, set this option to `0`:

        [chttpd]
        port = 0

  `prefer_minimal`

    If a request has the header `"Prefer": "return=minimal"`, CouchDB will only send the headers that are listed for the `prefer_minimal` configuration.:

        [chttpd]
        prefer_minimal = Cache-Control, Content-Length, Content-Range, Content-Type, ETag, Server, Transfer-Encoding, Vary

    Warning

    Removing the Server header from the settings will mean that the CouchDB server header is replaced with the MochiWeb server header.

  `authentication_handlers`

    List of authentication handlers used by CouchDB. You may extend them via third-party plugins or remove some of them if you won’t let users to use one of provided methods:

        [chttpd]
        authentication_handlers = {chttpd_auth, cookie_authentication_handler}, {chttpd_auth, default_authentication_handler}

    - `{chttpd_auth, cookie_authentication_handler}`: used for Cookie auth;
    - `{chttpd_auth, proxy_authentication_handler}`: used for Proxy auth;
    - `{chttpd_auth, jwt_authentication_handler}`: used for JWT auth;
    - `{chttpd_auth, default_authentication_handler}`: used for Basic auth;
    - `{couch_httpd_auth, null_authentication_handler}`: disables auth, breaks CouchDB.
  `buffer_response`

    Changed in version 3.1.1.

    Set this to `true` to delay the start of a response until the end has been calculated. This increases memory usage, but simplifies client error handling as it eliminates the possibility that a response may be deliberately terminated midway through, due to a timeout. This config value may be changed at runtime, without impacting any in-flight responses.

    Even if this is set to `false` (the default), buffered responses can be enabled on a per-request basis for any delayed JSON response call by adding `?buffer_response=true` to the request’s parameters.

  `allow_jsonp`

    Changed in version 3.2: moved from [httpd] to [chttpd] section

    The `true` value of this option enables JSONP support (it’s `false` by default):

        [chttpd]
        allow_jsonp = false

  `changes_timeout`

    Changed in version 3.2: moved from [httpd] to [chttpd] section

    Specifies default timeout value for Changes Feed in milliseconds (60000 by default):

        [chttpd]
        changes_timeout = 60000 ; 60 seconds

  `config_whitelist`

    Changed in version 3.2: moved from [httpd] to [chttpd] section

    Sets the configuration modification whitelist. Only whitelisted values may be changed via the config API. To allow the admin to change this value over HTTP, remember to include `{chttpd,config_whitelist}` itself. Excluding it from the list would require editing this file to update the whitelist:

        [chttpd]
        config_whitelist = [{chttpd,config_whitelist}, {log,level}, {etc,etc}]

  `enable_cors`

    New in version 1.3.

    Changed in version 3.2: moved from [httpd] to [chttpd] section

    Controls CORS feature:

        [chttpd]
        enable_cors = false

  `secure_rewrites`

    Changed in version 3.2: moved from [httpd] to [chttpd] section

    This option allow to isolate databases via subdomains:

        [chttpd]
        secure_rewrites = true

  `x_forwarded_host`

    Changed in version 3.2: moved from [httpd] to [chttpd] section

    The x_forwarded_host header (`X-Forwarded-Host` by default) is used to forward the original value of the `Host` header field in case, for example, if a reverse proxy is rewriting the “Host” header field to some internal host name before forward the request to CouchDB:

        [chttpd]
        x_forwarded_host = X-Forwarded-Host

    This header has higher priority above `Host` one, if only it exists in the request.

  `x_forwarded_proto`

    Changed in version 3.2: moved from [httpd] to [chttpd] section

    x_forwarded_proto header (`X-Forwarder-Proto` by default) is used for identifying the originating protocol of an HTTP request, since a reverse proxy may communicate with CouchDB instance using HTTP even if the request to the reverse proxy is HTTPS:

        [chttpd]
        x_forwarded_proto = X-Forwarded-Proto

  `x_forwarded_ssl`

    Changed in version 3.2: moved from [httpd] to [chttpd] section

    The x_forwarded_ssl header (`X-Forwarded-Ssl` by default) tells CouchDB that it should use the https scheme instead of the http. Actually, it’s a synonym for `X-Forwarded-Proto: https` header, but used by some reverse proxies:

        [chttpd]
        x_forwarded_ssl = X-Forwarded-Ssl

  `enable_xframe_options`

    Changed in version 3.2: moved from [httpd] to [chttpd] section

    Controls Enables or disabled feature:

        [chttpd]
        enable_xframe_options = false

  `max_http_request_size`

    Changed in version 3.2: moved from [httpd] to [chttpd] section

    Limit the maximum size of the HTTP request body. This setting applies to all requests and it doesn’t discriminate between single vs. multi-document operations. So setting it to 1MB would block a PUT of a document larger than 1MB, but it might also block a `_bulk_docs` update of 1000 1KB documents, or a multipart/related update of a small document followed by two 512KB attachments. This setting is intended to be used as a protection against maliciously large HTTP requests rather than for limiting maximum document sizes.

        [chttpd]
        max_http_request_size = 4294967296 ; 4 GB

    Warning

    Before version 2.1.0 `couchdb/max_document_size` was implemented effectively as `max_http_request_size`. That is, it checked HTTP request bodies instead of document sizes. After the upgrade, it is advisable to review the usage of these configuration settings.

`[httpd]`

  Changed in version 3.2: These options were moved to [chttpd] section: allow_jsonp, changes_timeout, config_whitelist, enable_cors, secure_rewrites, x_forwarded_host, x_forwarded_proto, x_forwarded_ssl, enable_xframe_options, max_http_request_size.

  `server_options`

    Server options for the MochiWeb component of CouchDB can be added to the configuration files:

        [httpd]
        server_options = [{backlog, 128}, {acceptor_pool_size, 16}]

    The options supported are a subset of full options supported by the TCP/IP stack. A list of the supported options are provided in the Erlang inet documentation.

  `socket_options`

    The socket options for the listening socket in CouchDB, as set at the beginning of ever request, can be specified as a list of tuples. For example:

        [httpd]
        socket_options = [{sndbuf, 262144}]

    The options supported are a subset of full options supported by the TCP/IP stack. A list of the supported options are provided in the Erlang inet documentation.

## 3.5.2. HTTPS (SSL/TLS) Options

`[ssl]`

  CouchDB supports TLS/SSL natively, without the use of a proxy server.

  HTTPS setup can be tricky, but the configuration in CouchDB was designed to be as easy as possible. All you need is two files; a certificate and a private key. If you have an official certificate from a certificate authority, both should be in your possession already.

  If you just want to try this out and don’t want to go through the hassle of obtaining an official certificate, you can create a self-signed certificate. Everything will work the same, but clients will get a warning about an insecure certificate.

  You will need the OpenSSL command line tool installed. It probably already is.

      shell> mkdir /etc/couchdb/cert
      shell> cd /etc/couchdb/cert
      shell> openssl genrsa > privkey.pem
      shell> openssl req -new -x509 -key privkey.pem -out couchdb.pem -days 1095
      shell> chmod 600 privkey.pem couchdb.pem
      shell> chown couchdb privkey.pem couchdb.pem

  Now, you need to edit CouchDB’s configuration, by editing your `local.ini` file. Here is what you need to do.

  Under the `[ssl]` section, enable HTTPS and set up the newly generated certificates:

      [ssl]
      enable = true
      cert_file = /etc/couchdb/cert/couchdb.pem
      key_file = /etc/couchdb/cert/privkey.pem

  For more information please read certificates HOWTO.

  Now start (or restart) CouchDB. You should be able to connect to it using HTTPS on port 6984:

      shell> curl https://127.0.0.1:6984/
      curl: (60) SSL certificate problem, verify that the CA cert is OK. Details:
      error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
      More details here: http://curl.haxx.se/docs/sslcerts.html

      curl performs SSL certificate verification by default, using a "bundle"
      of Certificate Authority (CA) public keys (CA certs). If the default
      bundle file isn't adequate, you can specify an alternate file
      using the --cacert option.
      If this HTTPS server uses a certificate signed by a CA represented in
      the bundle, the certificate verification probably failed due to a
      problem with the certificate (it might be expired, or the name might
      not match the domain name in the URL).
      If you'd like to turn off curl's verification of the certificate, use
      the -k (or --insecure) option.

  Oh no! What happened?! Remember, clients will notify their users that your certificate is self signed. `curl` is the client in this case and it notifies you. Luckily you trust yourself (don’t you?) and you can specify the `-k` option as the message reads:

      shell> curl -k https://127.0.0.1:6984/
      {"couchdb":"Welcome","version":"1.5.0"}

  All done.

  For performance reasons, and for ease of setup, you may still wish to terminate HTTPS connections at your load balancer / reverse proxy, then use unencrypted HTTP between it and your CouchDB cluster. This is a recommended approach.

  Additional detail may be available in the CouchDB wiki.

  `cacert_file`

    The path to a file containing PEM encoded CA certificates. The CA certificates are used to build the server certificate chain, and for client authentication. Also the CAs are used in the list of acceptable client CAs passed to the client when a certificate is requested. May be omitted if there is no need to verify the client and if there are not any intermediate CAs for the server certificate:

        [ssl]
        cacert_file = /etc/ssl/certs/ca-certificates.crt

  `cert_file`

    Path to a file containing the user’s certificate:

        [ssl]
        cert_file = /etc/couchdb/cert/couchdb.pem

  `key_file`

    Path to file containing user’s private PEM encoded key:

        [ssl]
        key_file = /etc/couchdb/cert/privkey.pem

  `password`

    String containing the user’s password. Only used if the private key file is password protected:

        [ssl]
        password = somepassword

  `ssl_certificate_max_depth`

    Maximum peer certificate depth (must be set even if certificate validation is off):

        [ssl]
        ssl_certificate_max_depth = 1

  `verify_fun`

    The verification fun (optional) if not specified, the default verification fun will be used:

        [ssl]
        verify_fun = {Module, VerifyFun}

  `verify_ssl_certificates`

    Set to `true` to validate peer certificates:

        [ssl]
        verify_ssl_certificates = false

  `fail_if_no_peer_cert`

    Set to `true` to terminate the TLS/SSL handshake with a `handshake_failure` alert message if the client does not send a certificate. Only used if `verify_ssl_certificates` is `true`. If set to `false` it will only fail if the client sends an invalid certificate (an empty certificate is considered valid):

        [ssl]
        fail_if_no_peer_cert = false

  `secure_renegotiate`

    Set to `true` to reject renegotiation attempt that does not live up to RFC 5746:

        [ssl]
        secure_renegotiate = true

  `ciphers`

    Set to the cipher suites that should be supported which can be specified in erlang format “{ecdhe_ecdsa,aes_128_cbc,sha256}” or in OpenSSL format “ECDHE-ECDSA-AES128-SHA256”.

        [ssl]
        ciphers = ["ECDHE-ECDSA-AES128-SHA256", "ECDHE-ECDSA-AES128-SHA"]

  `tls_versions`

    Set to a list of permitted SSL/TLS protocol versions:

        [ssl]
        tls_versions = [tlsv1 | 'tlsv1.1' | 'tlsv1.2']

## 3.5.3. Cross-Origin Resource Sharing

`[cors]`

  New in version 1.3: added CORS support, see JIRA COUCHDB-431

  Changed in version 3.2: moved from [httpd] to [chttpd] section

  CORS, or “Cross-Origin Resource Sharing”, allows a resource such as a web page running JavaScript inside a browser, to make AJAX requests (XMLHttpRequests) to a different domain, without compromising the security of either party.

  A typical use case is to have a static website hosted on a CDN make requests to another resource, such as a hosted CouchDB instance. This avoids needing an intermediary proxy, using JSONP or similar workarounds to retrieve and host content.

  While CouchDB’s integrated HTTP server has support for document attachments makes this less of a constraint for pure CouchDB projects, there are many cases where separating the static content from the database access is desirable, and CORS makes this very straightforward.

  By supporting CORS functionality, a CouchDB instance can accept direct connections to protected databases and instances, without the browser functionality being blocked due to same-origin constraints. CORS is supported today on over 90% of recent browsers.

  CORS support is provided as experimental functionality in 1.3, and as such will need to be enabled specifically in CouchDB’s configuration. While all origins are forbidden from making requests by default, support is available for simple requests, preflight requests and per-vhost configuration.

  This section requires `chttpd/enable_cors` option have `true` value:

      [chttpd]
      enable_cors = true

  `credentials`

    By default, neither authentication headers nor cookies are included in requests and responses. To do so requires both setting `XmlHttpRequest.withCredentials = true` on the request object in the browser and enabling credentials support in CouchDB.

        [cors]
        credentials = true

    CouchDB will respond to a credentials-enabled CORS request with an additional header, `Access-Control-Allow-Credentials=true`.

  `origins`

    List of origins separated by a comma, `*` means accept all. You can’t set `origins = *` and `credentials = true` option at the same time:

        [cors]
        origins = *

    Access can be restricted by protocol, host and optionally by port. Origins must follow the scheme: http://example.com:80:

        [cors]
        origins = http://localhost, https://localhost, http://couch.mydev.name:8080

    Note that by default, no origins are accepted. You must define them explicitly.

  `headers`

    List of accepted headers separated by a comma:

        [cors]
        headers = X-Couch-Id, X-Couch-Rev

  `methods`

    List of accepted methods:

        [cors]
        methods = GET,POST

  `max_age`

    Sets the `Access-Control-Max-Age` header in seconds. Use it to avoid repeated `OPTIONS` requests.

    > [cors] max_age = 3600

  See also

  Original JIRA implementation ticket

  Standards and References:

  - IETF RFCs relating to methods: RFC 2618, RFC 2817, RFC 5789
  - IETF RFC for Web Origins: RFC 6454
  - W3C CORS standard

  Mozilla Developer Network Resources:

  - Same origin policy for URIs
  - HTTP Access Control
  - Server-side Access Control
  - JavaScript same origin policy

  Client-side CORS support and usage:

  - CORS browser support matrix
  - COS tutorial
  - XHR with CORS

### 3.5.3.1. Per Virtual Host Configuration

Warning

Virtual Hosts are deprecated in CouchDB 3.0, and will be removed in CouchDB 4.0.

To set the options for a `vhosts`, you will need to create a section with the vhost name prefixed by `cors:`. Example case for the vhost example.com:

    [cors:example.com]
    credentials = false
    ; List of origins separated by a comma
    origins = *
    ; List of accepted headers separated by a comma
    headers = X-CouchDB-Header
    ; List of accepted methods
    methods = HEAD, GET

A video from 2010 on vhost and rewrite configuration is available, but is not guaranteed to match current syntax or behaviour.

## 3.5.4. Virtual Hosts

Warning

Virtual Hosts are deprecated in CouchDB 3.0, and will be removed in CouchDB 4.0.

`[vhosts]`

  CouchDB can map requests to different locations based on the `Host` header, even if they arrive on the same inbound IP address.

  This allows different virtual hosts on the same machine to map to different databases or design documents, etc. The most common use case is to map a virtual host to a Rewrite Handler, to provide full control over the application’s URIs.

  To add a virtual host, add a CNAME pointer to the DNS for your domain name. For development and testing, it is sufficient to add an entry in the hosts file, typically /etc/hosts` on Unix-like operating systems:

      # CouchDB vhost definitions, refer to local.ini for further details
      127.0.0.1       couchdb.local

  Test that this is working:

      $ ping -n 2 couchdb.local
      PING couchdb.local (127.0.0.1) 56(84) bytes of data.
      64 bytes from localhost (127.0.0.1): icmp_req=1 ttl=64 time=0.025 ms
      64 bytes from localhost (127.0.0.1): icmp_req=2 ttl=64 time=0.051 ms

  Finally, add an entry to your configuration file in the `[vhosts]` section:

      [vhosts]
      couchdb.local:5984 = /example
      *.couchdb.local:5984 = /example

  If your CouchDB is listening on the the default HTTP port (80), or is sitting behind a proxy, then you don’t need to specify a port number in the `vhost` key.

  The first line will rewrite the request to display the content of the example database. This rule works only if the `Host` header is `couchdb.local` and won’t work for CNAMEs. The second rule, on the other hand, matches all CNAMEs to example db, so that both www.couchdb.local and db.couchdb.local will work.

### 3.5.4.1. Rewriting Hosts to a Path

Like in the _rewrite handler you can match some variable and use them to create the target path. Some examples:

    [vhosts]
    *.couchdb.local = /*
    :dbname. = /:dbname
    :ddocname.:dbname.example.com = /:dbname/_design/:ddocname/_rewrite

The first rule passes the wildcard as `dbname`. The second one does the same, but uses a variable name. And the third one allows you to use any URL with `ddocname` in any database with `dbname`.

## 3.5.5. X-Frame-Options

X-Frame-Options is a response header that controls whether a http response can be embedded in a <frame>, <iframe> or <object>. This is a security feature to help against clickjacking.

> [x_frame_options] ; Settings same-origin will return X-Frame-Options: SAMEORIGIN. ; If same origin is set, it will ignore the hosts setting ; same_origin = true ; Settings hosts will ; return X-Frame-Options: ALLOW-FROM https://example.com/ ; List of hosts separated by a comma. * means accept all ; hosts =

If xframe_options is enabled it will return `X-Frame-Options: DENY` by default. If `same_origin` is enabled it will return `X-Frame-Options: SAMEORIGIN`. A `X-FRAME-OPTIONS: ALLOW-FROM url` will be returned when `same_origin` is false, and the HOST header matches one of the urls in the `hosts` config. Otherwise a `X-Frame-Options: DENY` will be returned.