3.5. CouchDB HTTP Server¶

3.5.1. HTTP Server Options¶

[httpd]¶

Warning

In CouchDB 2.x, the httpd section mostly refers to the node-local port, on port 5986 by default. This port is used only for maintenance and administrative tasks. It should not be used for regular CouchDB access, and for security reasons, should always be bound to localhost (127.0.0.1) or a private LAN segment only.

allow_jsonp¶

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

[httpd]
allow_jsonp = false

bind_address¶

Defines the IP address by which the node-local port is available. The recommended setting is always:

[httpd]
bind_address = 127.0.0.1

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

[httpd]
bind_address = ::1

changes_timeout¶

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

[httpd]
changes_feed = 60000 ; 60 seconds

config_whitelist¶

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 {httpd,config_whitelist} itself. Excluding it from the list would require editing this file to update the whitelist:

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

default_handler¶

Specifies default HTTP requests handler:

[httpd]
default_handler = {couch_httpd_db, handle_request}

enable_cors¶

New in version 1.3.

Controls CORS feature:

[httpd]
enable_cors = false

port¶

Defines the port number to listen:

[httpd]
port = 5984

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

[httpd]
port = 0

redirect_vhost_handler¶

This option customizes the default function that handles requests to virtual hosts:

[httpd]
redirect_vhost_handler = {Module, Fun}

The specified function take 2 arguments: the MochiWeb request object and the target path.

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}]

secure_rewrites¶

This option allow to isolate databases via subdomains:

[httpd]
secure_rewrites = true

socket_options¶

The socket options for the listening socket in CouchDB can be specified as a list of tuples. For example:

[httpd]
socket_options = [{recbuf, 262144}, {sndbuf, 262144}, {nodelay, true}]

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.

vhost_global_handlers¶

List of global handlers that are available for virtual hosts:

[httpd]
vhost_global_handlers = _utils, _uuids, _session, _users

x_forwarded_host¶

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:

[httpd]
x_forwarded_host = X-Forwarded-Host

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

x_forwarded_proto¶

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:

[httpd]
x_forwarded_proto = X-Forwarded-Proto

x_forwarded_ssl¶

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:

[httpd]
x_forwarded_ssl = X-Forwarded-Ssl

enable_xframe_options¶

Controls Enables or disabled feature:

[httpd]
enable_xframe_options = false

WWW-Authenticate¶

Set this option to trigger basic-auth pop-up on unauthorized requests:

[httpd]
WWW-Authenticate = Basic realm="Welcome to the Couch!"

max_http_request_size¶

Changed in version 2.1.0.

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.

[httpd]
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.

[chttpd]¶

Note

In CouchDB 2.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.

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 = {couch_httpd_auth, cookie_authentication_handler}, {couch_httpd_auth, default_authentication_handler}

{couch_httpd_auth, cookie_authentication_handler}: used for Cookie auth;
{couch_httpd_auth, proxy_authentication_handler}: used for Proxy auth;
{couch_httpd_auth, default_authentication_handler}: used for Basic auth;
{couch_httpd_auth, null_authentication_handler}: disables auth. Everlasting Admin Party!

3.5.2. Secure Socket Level Options¶

[ssl]¶

CouchDB supports SSL natively. All your secure connection needs can now be served without needing to set up and maintain a separate proxy server that handles SSL.

SSL 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 bought an official SSL 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 pay anything upfront, 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.

At first, enable the HTTPS daemon:

[daemons]
httpsd = {chttpd, start_link, [https]}

Next, under the [ssl] section set up the newly generated certificates:

[ssl]
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.

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

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 httpd/enable_cors option have true value:

[httpd]
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

Per Virtual Host Configuration¶

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

3.5.4. Virtual Hosts¶

[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.

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.

You could also change the default function to handle request by changing the setting httpd/redirect_vhost_handler.

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.