Description

The hosts plugin is useful for serving zones from a /etc/hosts file. It serves from a preloaded file that exists on disk. It checks the file for changes and updates the zones accordingly. This plugin only supports A, AAAA, and PTR records. The hosts plugin can be used with readily available hosts files that block access to advertising servers.

The plugin reloads the content of the hosts file every 5 seconds. Upon reload, CoreDNS will use the new definitions. Should the file be deleted, any inlined content will continue to be served. When the file is restored, it will then again be used.

If you want to pass the request to the rest of the plugin chain if there is no match in the hosts plugin, you must specify the fallthrough option.

This plugin can only be used once per Server Block.

The hosts file

Commonly the entries are of the form IP_address canonical_hostname [aliases...] as explained by the hosts(5) man page.

Examples:

# The following lines are desirable for IPv4 capable hosts
127.0.0.1       localhost
192.168.1.10    example.com            example

# The following lines are desirable for IPv6 capable hosts
::1                     localhost ip6-localhost ip6-loopback
fdfc:a744:27b5:3b0e::1  example.com example

PTR records

PTR records for reverse lookups are generated automatically by CoreDNS (based on the hosts file entries) and cannot be created manually.

Syntax

hosts [FILE [ZONES...]] {
    [INLINE]
    ttl SECONDS
    no_reverse
    reload DURATION
    fallthrough [ZONES...]
}

• FILE the hosts file to read and parse. If the path is relative the path from the root plugin will be prepended to it. Defaults to /etc/hosts if omitted. We scan the file for changes every 5 seconds.
• ZONES zones it should be authoritative for. If empty, the zones from the configuration block are used.
• INLINE the hosts file contents inlined in Corefile. If there are any lines before fallthrough then all of them will be treated as the additional content for hosts file. The specified hosts file path will still be read but entries will be overridden.
• ttl change the DNS TTL of the records generated (forward and reverse). The default is 3600 seconds (1 hour).
• reload change the period between each hostsfile reload. A time of zero seconds disables the feature. Examples of valid durations: “300ms”, “1.5h” or “2h45m”. See Go’s time. package.
• no_reverse disable the automatic generation of the in-addr.arpa or ip6.arpa entries for the hosts
• fallthrough If zone matches and no record can be generated, pass request to the next plugin. If [ZONES…] is omitted, then fallthrough happens for all zones for which the plugin is authoritative. If specific zones are listed (for example in-addr.arpa and ip6.arpa), then only queries for those zones will be subject to fallthrough.

Metrics

If monitoring is enabled (via the prometheus plugin) then the following metrics are exported:

• coredns_hosts_entries{} - The combined number of entries in hosts and Corefile.
• coredns_hosts_reload_timestamp_seconds{} - The timestamp of the last reload of hosts file.

Examples

Load /etc/hosts file.

. {
    hosts
}

Load example.hosts file in the current directory.

. {
    hosts example.hosts
}

Load example.hosts file and only serve example.org and example.net from it and fall through to the next plugin if query doesn’t match.

. {
    hosts example.hosts example.org example.net {
        fallthrough
    }
}

Load hosts file inlined in Corefile.

example.hosts example.org {
    hosts {
        10.0.0.1 example.org
        fallthrough
    }
    whoami
}

See also

The form of the entries in the /etc/hosts file are based on IETF RFC 952 which was updated by IETF RFC 1123.