{ "source": "doc/api/dns.md", "modules": [ { "textRaw": "DNS", "name": "dns", "stability": 2, "stabilityText": "Stable", "desc": "

The dns module contains functions belonging to two different categories:

\n

1) Functions that use the underlying operating system facilities to perform\nname resolution, and that do not necessarily perform any network communication.\nThis category contains only one function: dns.lookup(). Developers\nlooking to perform name resolution in the same way that other applications on\nthe same operating system behave should use dns.lookup().

\n

For example, looking up iana.org.

\n
const dns = require('dns');\n\ndns.lookup('iana.org', (err, address, family) => {\n  console.log('address: %j family: IPv%s', address, family);\n});\n// address: "192.0.43.8" family: IPv4\n
\n

2) Functions that connect to an actual DNS server to perform name resolution,\nand that always use the network to perform DNS queries. This category\ncontains all functions in the dns module except dns.lookup(). These\nfunctions do not use the same set of configuration files used by\ndns.lookup() (e.g. /etc/hosts). These functions should be used by\ndevelopers who do not want to use the underlying operating system's facilities\nfor name resolution, and instead want to always perform DNS queries.

\n

Below is an example that resolves 'archive.org' then reverse resolves the IP\naddresses that are returned.

\n
const dns = require('dns');\n\ndns.resolve4('archive.org', (err, addresses) => {\n  if (err) throw err;\n\n  console.log(`addresses: ${JSON.stringify(addresses)}`);\n\n  addresses.forEach((a) => {\n    dns.reverse(a, (err, hostnames) => {\n      if (err) {\n        throw err;\n      }\n      console.log(`reverse for ${a}: ${JSON.stringify(hostnames)}`);\n    });\n  });\n});\n
\n

There are subtle consequences in choosing one over the other, please consult\nthe Implementation considerations section for more information.

\n", "methods": [ { "textRaw": "dns.getServers()", "type": "method", "name": "getServers", "meta": { "added": [ "v0.11.3" ], "changes": [] }, "desc": "

Returns an array of IP address strings that are being used for name\nresolution.

\n", "signatures": [ { "params": [] } ] }, { "textRaw": "dns.lookup(hostname[, options], callback)", "type": "method", "name": "lookup", "meta": { "added": [ "v0.1.90" ], "changes": [ { "version": "v1.2.0", "pr-url": "https://github.com/nodejs/node/pull/744", "description": "The `all` option is supported now." } ] }, "desc": "

Resolves a hostname (e.g. 'nodejs.org') into the first found A (IPv4) or\nAAAA (IPv6) record. options can be an object or integer. If options is\nnot provided, then IPv4 and IPv6 addresses are both valid. If options is\nan integer, then it must be 4 or 6.

\n

Alternatively, options can be an object containing these properties:

\n\n

All properties are optional.

\n

The callback function has arguments (err, address, family). address is a\nstring representation of an IPv4 or IPv6 address. family is either the\ninteger 4 or 6 and denotes the family of address (not necessarily the\nvalue initially passed to lookup).

\n

With the all option set to true, the arguments change to\n(err, addresses), with addresses being an array of objects with the\nproperties address and family.

\n

On error, err is an Error object, where err.code is the error code.\nKeep in mind that err.code will be set to 'ENOENT' not only when\nthe hostname does not exist but also when the lookup fails in other ways\nsuch as no available file descriptors.

\n

dns.lookup() does not necessarily have anything to do with the DNS protocol.\nThe implementation uses an operating system facility that can associate names\nwith addresses, and vice versa. This implementation can have subtle but\nimportant consequences on the behavior of any Node.js program. Please take some\ntime to consult the Implementation considerations section before using\ndns.lookup().

\n

Example usage:

\n
const dns = require('dns');\nconst options = {\n  family: 6,\n  hints: dns.ADDRCONFIG | dns.V4MAPPED,\n};\ndns.lookup('example.com', options, (err, address, family) =>\n  console.log('address: %j family: IPv%s', address, family));\n// address: "2606:2800:220:1:248:1893:25c8:1946" family: IPv6\n\n// When options.all is true, the result will be an Array.\noptions.all = true;\ndns.lookup('example.com', options, (err, addresses) =>\n  console.log('addresses: %j', addresses));\n// addresses: [{"address":"2606:2800:220:1:248:1893:25c8:1946","family":6}]\n
\n", "modules": [ { "textRaw": "Supported getaddrinfo flags", "name": "supported_getaddrinfo_flags", "desc": "

The following flags can be passed as hints to dns.lookup().

\n\n", "type": "module", "displayName": "Supported getaddrinfo flags" } ], "signatures": [ { "params": [ { "name": "hostname" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "dns.lookupService(address, port, callback)", "type": "method", "name": "lookupService", "meta": { "added": [ "v0.11.14" ], "changes": [] }, "desc": "

Resolves the given address and port into a hostname and service using\nthe operating system's underlying getnameinfo implementation.

\n

If address is not a valid IP address, a TypeError will be thrown.\nThe port will be coerced to a number. If it is not a legal port, a TypeError\nwill be thrown.

\n

The callback has arguments (err, hostname, service). The hostname and\nservice arguments are strings (e.g. 'localhost' and 'http' respectively).

\n

On error, err is an Error object, where err.code is the error code.

\n
const dns = require('dns');\ndns.lookupService('127.0.0.1', 22, (err, hostname, service) => {\n  console.log(hostname, service);\n  // Prints: localhost ssh\n});\n
\n", "signatures": [ { "params": [ { "name": "address" }, { "name": "port" }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolve(hostname[, rrtype], callback)", "type": "method", "name": "resolve", "meta": { "added": [ "v0.1.27" ], "changes": [] }, "desc": "

Uses the DNS protocol to resolve a hostname (e.g. 'nodejs.org') into an\narray of the record types specified by rrtype.

\n

Valid values for rrtype are:

\n\n

The callback function has arguments (err, addresses). When successful,\naddresses will be an array, except when resolving an SOA record which returns\nan object structured in the same manner as one returned by the\ndns.resolveSoa() method. The type of each item in addresses is\ndetermined by the record type, and described in the documentation for the\ncorresponding lookup methods.

\n

On error, err is an Error object, where err.code is\none of the error codes listed here.

\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "rrtype", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolve4(hostname[, options], callback)", "type": "method", "name": "resolve4", "meta": { "added": [ "v0.1.16" ], "changes": [ { "version": "v7.2.0", "pr-url": "https://github.com/nodejs/node/pull/9296", "description": "This method now supports passing `options`, specifically `options.ttl`." } ] }, "desc": "

Uses the DNS protocol to resolve a IPv4 addresses (A records) for the\nhostname. The addresses argument passed to the callback function\nwill contain an array of IPv4 addresses (e.g.\n['74.125.79.104', '74.125.79.105', '74.125.79.106']).

\n\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolve6(hostname[, options], callback)", "type": "method", "name": "resolve6", "meta": { "added": [ "v0.1.16" ], "changes": [ { "version": "v7.2.0", "pr-url": "https://github.com/nodejs/node/pull/9296", "description": "This method now supports passing `options`, specifically `options.ttl`." } ] }, "desc": "

Uses the DNS protocol to resolve a IPv6 addresses (AAAA records) for the\nhostname. The addresses argument passed to the callback function\nwill contain an array of IPv6 addresses.

\n\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "options", "optional": true }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolveCname(hostname, callback)", "type": "method", "name": "resolveCname", "meta": { "added": [ "v0.3.2" ], "changes": [] }, "desc": "

Uses the DNS protocol to resolve CNAME records for the hostname. The\naddresses argument passed to the callback function\nwill contain an array of canonical name records available for the hostname\n(e.g. ['bar.example.com']).

\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolveMx(hostname, callback)", "type": "method", "name": "resolveMx", "meta": { "added": [ "v0.1.27" ], "changes": [] }, "desc": "

Uses the DNS protocol to resolve mail exchange records (MX records) for the\nhostname. The addresses argument passed to the callback function will\ncontain an array of objects containing both a priority and exchange\nproperty (e.g. [{priority: 10, exchange: 'mx.example.com'}, ...]).

\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolveNaptr(hostname, callback)", "type": "method", "name": "resolveNaptr", "meta": { "added": [ "v0.9.12" ], "changes": [] }, "desc": "

Uses the DNS protocol to resolve regular expression based records (NAPTR\nrecords) for the hostname. The callback function has arguments\n(err, addresses). The addresses argument passed to the callback function\nwill contain an array of objects with the following properties:

\n\n

For example:

\n
{\n  flags: 's',\n  service: 'SIP+D2U',\n  regexp: '',\n  replacement: '_sip._udp.example.com',\n  order: 30,\n  preference: 100\n}\n
\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolveNs(hostname, callback)", "type": "method", "name": "resolveNs", "meta": { "added": [ "v0.1.90" ], "changes": [] }, "desc": "

Uses the DNS protocol to resolve name server records (NS records) for the\nhostname. The addresses argument passed to the callback function will\ncontain an array of name server records available for hostname\n(e.g. ['ns1.example.com', 'ns2.example.com']).

\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolvePtr(hostname, callback)", "type": "method", "name": "resolvePtr", "meta": { "added": [ "v6.0.0" ], "changes": [] }, "desc": "

Uses the DNS protocol to resolve pointer records (PTR records) for the\nhostname. The addresses argument passed to the callback function will\nbe an array of strings containing the reply records.

\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolveSoa(hostname, callback)", "type": "method", "name": "resolveSoa", "meta": { "added": [ "v0.11.10" ], "changes": [] }, "desc": "

Uses the DNS protocol to resolve a start of authority record (SOA record) for\nthe hostname. The addresses argument passed to the callback function will\nbe an object with the following properties:

\n\n
{\n  nsname: 'ns.example.com',\n  hostmaster: 'root.example.com',\n  serial: 2013101809,\n  refresh: 10000,\n  retry: 2400,\n  expire: 604800,\n  minttl: 3600\n}\n
\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolveSrv(hostname, callback)", "type": "method", "name": "resolveSrv", "meta": { "added": [ "v0.1.27" ], "changes": [] }, "desc": "

Uses the DNS protocol to resolve service records (SRV records) for the\nhostname. The addresses argument passed to the callback function will\nbe an array of objects with the following properties:

\n\n
{\n  priority: 10,\n  weight: 5,\n  port: 21223,\n  name: 'service.example.com'\n}\n
\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "callback" } ] } ] }, { "textRaw": "dns.resolveTxt(hostname, callback)", "type": "method", "name": "resolveTxt", "meta": { "added": [ "v0.1.27" ], "changes": [] }, "desc": "

Uses the DNS protocol to resolve text queries (TXT records) for the\nhostname. The addresses argument passed to the callback function is\nis a two-dimensional array of the text records available for hostname (e.g.,\n[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]). Each sub-array contains TXT chunks of\none record. Depending on the use case, these could be either joined together or\ntreated separately.

\n", "signatures": [ { "params": [ { "name": "hostname" }, { "name": "callback" } ] } ] }, { "textRaw": "dns.reverse(ip, callback)", "type": "method", "name": "reverse", "meta": { "added": [ "v0.1.16" ], "changes": [] }, "desc": "

Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an\narray of hostnames.

\n

The callback function has arguments (err, hostnames), where hostnames\nis an array of resolved hostnames for the given ip.

\n

On error, err is an Error object, where err.code is\none of the DNS error codes.

\n", "signatures": [ { "params": [ { "name": "ip" }, { "name": "callback" } ] } ] }, { "textRaw": "dns.setServers(servers)", "type": "method", "name": "setServers", "meta": { "added": [ "v0.11.3" ], "changes": [] }, "desc": "

Sets the IP addresses of the servers to be used when resolving. The servers\nargument is an array of IPv4 or IPv6 addresses.

\n

If a port specified on the address it will be removed.

\n

An error will be thrown if an invalid address is provided.

\n

The dns.setServers() method must not be called while a DNS query is in\nprogress.

\n", "signatures": [ { "params": [ { "name": "servers" } ] } ] } ], "modules": [ { "textRaw": "Error codes", "name": "error_codes", "desc": "

Each DNS query can return one of the following error codes:

\n\n", "type": "module", "displayName": "Error codes" }, { "textRaw": "Implementation considerations", "name": "implementation_considerations", "desc": "

Although dns.lookup() and the various dns.resolve*()/dns.reverse()\nfunctions have the same goal of associating a network name with a network\naddress (or vice versa), their behavior is quite different. These differences\ncan have subtle but significant consequences on the behavior of Node.js\nprograms.

\n", "modules": [ { "textRaw": "`dns.lookup()`", "name": "`dns.lookup()`", "desc": "

Under the hood, dns.lookup() uses the same operating system facilities\nas most other programs. For instance, dns.lookup() will almost always\nresolve a given name the same way as the ping command. On most POSIX-like\noperating systems, the behavior of the dns.lookup() function can be\nmodified by changing settings in nsswitch.conf(5) and/or resolv.conf(5),\nbut note that changing these files will change the behavior of all other\nprograms running on the same operating system.

\n

Though the call to dns.lookup() will be asynchronous from JavaScript's\nperspective, it is implemented as a synchronous call to getaddrinfo(3) that\nruns on libuv's threadpool. Because libuv's threadpool has a fixed size, it\nmeans that if for whatever reason the call to getaddrinfo(3) takes a long\ntime, other operations that could run on libuv's threadpool (such as filesystem\noperations) will experience degraded performance. In order to mitigate this\nissue, one potential solution is to increase the size of libuv's threadpool by\nsetting the 'UV_THREADPOOL_SIZE' environment variable to a value greater than\n4 (its current default value). For more information on libuv's threadpool, see\nthe official libuv documentation.

\n", "type": "module", "displayName": "`dns.lookup()`" }, { "textRaw": "`dns.resolve()`, `dns.resolve*()` and `dns.reverse()`", "name": "`dns.resolve()`,_`dns.resolve*()`_and_`dns.reverse()`", "desc": "

These functions are implemented quite differently than dns.lookup(). They\ndo not use getaddrinfo(3) and they always perform a DNS query on the\nnetwork. This network communication is always done asynchronously, and does not\nuse libuv's threadpool.

\n

As a result, these functions cannot have the same negative impact on other\nprocessing that happens on libuv's threadpool that dns.lookup() can have.

\n

They do not use the same set of configuration files than what dns.lookup()\nuses. For instance, they do not use the configuration from /etc/hosts.

\n", "type": "module", "displayName": "`dns.resolve()`, `dns.resolve*()` and `dns.reverse()`" } ], "type": "module", "displayName": "Implementation considerations" } ], "type": "module", "displayName": "DNS" } ] }