rescached

RESCACHED(1)
============
M. Shulhan
2018.09.29
:doctype: manpage
:mansource: rescached
:manmanual: rescached


== NAME

rescached - DNS resolver cache daemon.


== SYNOPSIS

+rescached+ [-config 'rescached.cfg']


== OPTIONS

'rescached.cfg' is rescached configuration, usually it reside in
/etc/rescached/rescached.cfg.


== DESCRIPTION

+rescached+ is a daemon that caching internet name and address on local memory
for speeding up DNS resolution.

+rescached+ is not a reimplementation of DNS server like BIND.

+rescached+ primary goal is only to caching DNS queries and answers, used by
personal or small group of users, to minimize unneeded traffic to outside
network.


=== FEATURES

List of current features,

- Enable to handle request from UDP and TCP connections
- Enable to forward request using UDP or TCP
- Load and serve addresses and hostnames in +/etc/hosts+
- Load and serve hosts formatted files inside directory
  +/etc/rescached/hosts.d/+
- Blocking ads and/or malicious websites through host list in
  +/etc/rescached/hosts.d/hosts.block+
- Support loading and serving master (zone) file format from
  +/etc/rescached/master.d+
- Integration with openresolv
- Support DNS over HTTPS (DoH) (RFC 8484)


=== BEHIND THE DNS

When you open a website, let say 'kilabit.info', in a browser, the first thing
that browser do is to translate name address 'kilabit.info' into an internet
address (for example to 35.240.172.103) so browser can make a connection to
'kilabit.info' server.

How browser do that?

First, it will send query to one of DNS server listed in your system
configuration (in example, +/etc/resolv.conf+ in Linux).
Then, if your DNS server also "caching" the name that you requested, it will
reply the answer (internet address) directly, if it is not then it will ask
their parent DNS server.

----
+----+      +----------------+      +------------------+
| PC | <==> | ISP DNS Server | <==> | Other DNS Server | <==> ...
+----+      +----------------+      +------------------+
----

If you browsing frequently on the same site, hitting the refresh button,
opening another page on the same website, etc; this procedures will always
repeated every times, not including all external links like ads, social media
button, or JavaScript from an other server.

To make this repetitive procedures less occurred, you can run +rescached+ in
your personal computer.
The first time the answer is received in your local computer, +rescached+ will
saved it in computer memory and any subsequent request of the same address
will be answered directly by +rescached+.

----
+----+      +----------------+      +------------------+
| PC |      | ISP DNS Server | <==> | Other DNS Server | <==> ...
+----+      +----------------+      +------------------+
  ^^             ^^
  ||             ||
  vv             ||
+-----------+    ||
| rescached | <==//
+-----------+
----

The only request that will be send to your DNS server is the one that does not
already exist in +rescached+ cache.


=== HOW CACHE WORKS

This section explain the simplified version of how internal program works.

Each DNS record in cache have the time last accessed field, which defined how
the cache will be ordered in memory.
The last queried host-name will be at the bottom of cache list, and the oldest
queried host-name will at the top of cache list.

The following table illustrate list of caches in memory,

----
+---------------------+------------------+
| Accessed At         | host-name        |
+---------------------+------------------+
| 2018-01-01 00:00:01 | kilabit.info     |
+---------------------+------------------+
| 2018-01-01 00:00:02 | www.google.com   |
+---------------------+------------------+
|         ...         |        ...       |
+---------------------+------------------+
| 2018-01-01 00:01:00 | www.kilabit.info |
+---------------------+------------------+
----

Every +cache.prune_delay+ (let say every 5 minutes), rescached will try to
pruning old records from cache.
If the accessed-at value of record in cache is less than,

----
	current-time + cache.threshold
----

(remember that "+cache.threshold+" value must be negative) it will remove the
record from cache.


== BUILDING

=== PREREQUISITES

* https://golang.org[Go compiler]
* https://git-scm.com[git, version control system]
* asciidoc, to generate manual pages
* systemd or system V init tool for service on Linux

=== COMPILING

Steps to compile from source,

----
	$ go get -u github.com/shuLhan/rescached-go
	$ cd ${GOPATH}/src/github.com/shuLhan/rescached-go
	$ go build ./cmd/rescached
----

The last command will build binary named +rescached+ in current directory.

=== INSTALLATION

After program successfully build, you can install it manually by copying to
system binary directory.

==== MANUAL INSTALLATION

* Copy rescached configuration to system directory.
We use directory "/etc/rescached" as configuration directory.
+
	$ sudo mkdir -p /etc/rescached
	$ sudo cp cmd/rescached/rescached.cfg /etc/rescached/

* Copy rescached program to your system path.
+
	$ sudo cp -f rescached /usr/bin/

* Create system startup script.
+
If you want your program running each time the system is starting up you can
create a system startup script (or system service).
For OS using systemd, you can see an example for +systemd+ service in
+scripts/rescached.service+.
For system using launchd (macOS), you can see an example in
+scripts/info.kilabit.rescached.plist+.
+
This step could be different between systems, consult your distribution
wiki, forum, or mailing-list on how to create system startup script.

====  AUTOMATIC INSTALLATION ON LINUX

Automatic installation on Linux require systemd.
Run the following command

	$ sudo make install

to setup and copies all required files and binaries to system directories.
You can then start the rescached service using systemd,

	$ sudo systemctl start rescached

====  AUTOMATIC INSTALLATION ON MACOS

Run the following command

	$ sudo make install-macos

to setup and copies all required files and binaries to system directories.
You can then load the rescached service using launchd,

	$ sudo launchctl load info.kilabit.rescached


==== POST INSTALLATION

* Set your parent DNS server.
+
Edit rescached configuration, +/etc/rescached/rescached.cfg+, change the value
of +parent+ based on your preferred DNS server.

* Set the cache prune delay and threshold
+
Edit rescached configuration, +/etc/rescached/rescached.cfg+, change the value
of +cache.prune_delay+ and/or +cache.threshold+ to match your needs.

* Set your system DNS server to point to rescached.
+
In UNIX system,
+
	$ sudo mv /etc/resolv.conf /etc/resolv.conf.org
	$ sudo echo "nameserver 127.0.0.1" > /etc/resolv.conf

* If you use +systemd+, run +rescached+ service by invoking,
+
	$ sudo systemctl start rescached.service
+
and if you want +rescached+ service to run when system startup, enable it by
invoking,
+
	$ sudo systemctl enable rescached.service


== CONFIGURATION

All rescached configuration located in file +/etc/rescached/rescached.cfg+.
See manual page of *rescached.cfg*(5) for more information.

=== MASTER FILE

Rescached support loading master file format.
Unlike hosts file format, where each domain name is only mapped to type A
(IPv4 address), in master file, one can define other type that known to
rescached.
All files defined +dir.master+ configuration are considered as master file and
will be loaded by rescached only if the configuration is not empty.

Example of master file,

----
$ORIGIN my-site.vm.
$TTL    3600

; resource record (RR) address
@ A 192.168.56.10

; resource record alias
dev CNAME @

; resource record address for other sub-domain
staging A 192.168.100.1

; resource record address for other absolute domain.
my-site.com A 10.8.0.1
----

Here we defined the variable origin for root domain "my-site.vm." with minimum
time-to-live (TTL) to 3600 seconds.
If no "$ORIGIN" variable is defined, rescached will use the file name as
$ORIGIN's value.

The "@" character will be replaced with the value of $ORIGIN.

The first resource record (RR) is defining an IPv4 address for "my-site.vm."
to "192.168.56.10".

The second RR add an alias for relative subdomain "dev".
Domain name that does not terminated with "." are called relative, and
the origin will be appended to form the absolute domain "dev.my-site.vm".
In this case IP address for "dev.my-site.vm." is equal to "my-site.vm.".

The third RR define a mapping for another relative subdomain
"staging.my-site.vm." to address "192.168.100.1".

The last RR define a mapping for absolute domain "my-site.com." to IP
address "10.8.0.1".

For more information about format of master file see RFC 1035 section 5.


=== INTEGRATION WITH OPENRESOLV

Rescached can detect change on file generated by resolvconf.
To use this feature unset the "file.resolvconf" in configuration file and set
either "dnsmasq_resolv", "pdnsd_resolv", or "unbound_conf" in
"/etc/resolvconf.conf" to point to file referenced in "file.resolvconf".

For more information see  *rescached.cfg*(5).


=== INTEGRATION WITH DNS OVER HTTPS

DNS over HTTPS (DoH) is the new protocol to query DNS through HTTPS layer.
Rescached support serving DNS over HTTPS or as client to parent DoH
nameservers.
To enable this feature rescached provided TLS certificate and private key.

Example configuration in *rescached.cfg*,

----
	[dns "server"]
	parent = https://kilabit.info/dns-query
	tls.certificate = /etc/rescached/localhost.cert.pem
	tls.private_key = /etc/rescached/localhost.key.pem
	tls.allow_insecure = false
----

If the parent nameserver is using self-signed certificate, you can set
"tls.allow_insecure" to true.

Using the above configuration, rescached will serve DoH queries on
*https://localhost/dns-query* on port 443 and UDP queries on port 53.
All queries to both locations will be forwarded to parent nameserver.

This feature can be tested using Firefox Nightly by updating the configuration
in "about:config" into,

----
	network.trr.bootstrapAddress;127.0.0.1
	network.trr.mode;3
	network.trr.uri;https://localhost/dns-query
----

Since we are using `mode=3`, the `network.trr.bootstrapAddress` is required so
Firefox Nightly can resolve "localhost" to "127.0.0.1".
If you use the provided self-signed certificate, you must import and/or enable
an exception for it manually in Firefox Nightly (for example. by opening
`https://localhost/dns-query` in new tab and accept security risk).

To check if DoH works, first, set the `debug` option to `1`, and
restart the rescached.
Open a new terminal and run `sudo journalctl -xf`, to show current system log.
Run Firefox Nightly and open any random website.
At the terminal you will see output from rescached which looks like these,

----
... rescached[808]: dns: ^ DoH https://kilabit.info/dns-query 41269:&{Name:id.wikipedia.org Type:A}                                                                         
... rescached[808]: dns: < UDP 45873:&{Name:id.wikipedia.org Type:AAAA}                                                                                                     
... rescached[808]: dns: + UDP 41269:&{Name:id.wikipedia.org Type:A}     
----

If you see number "4" in request line, "< request: 4", thats indicated that
request is from HTTPS connection and its working.


== EXIT STATUS

Upon success, +rescached+ will return 0, or 1 otherwise.


== FILES

'/etc/rescached/rescached.cfg'::

The +rescached+ main configuration.
This configuration will be read when program started.

'/usr/share/rescached/LICENSE'::

License file for this software.

'/var/run/rescached.pid'::

File where process ID of rescached will be saved when running.


== NOTES

This program developed with references to,

'RFC1034':: Domain Names - Concepts and Facilities.
'RFC1035':: Domain Names - Implementation and Specification.
'RFC1886':: DNS Extensions to support IP version 6.
'RFC2782':: A DNS RR for specifying the location of services (DNS SRV)
'RFC8484':: DNS Queries over HTTPS (DoH)

== BUGS

+rescached+ only know specific DNS record type,
[horizontal]
A:: A host address in IPv4
NS:: An authoritative name server
CNAME:: A canonical name for an alias
SOA::  Start of [a zone of] authority record
MB:: Mail box
MG:: Mail group
NULL:: Placeholders for experimental extensions
WKS:: Record to describe well-known services supported by a host
PTR:: Pointer to a canonical name.
HINFO:: Host information
MINFO:: Mail information
MX:: Mail exchange
TXT:: Text record
AAAA:: A host address in IPv6
SRV:: Service locator
OPT:: This is a "pseudo DNS record type" needed to support EDNS

+rescached+ only run and tested in Linux and macOS system.
Technically, if it can compiled, it will run in any operating system.

For request of features and/or bugs report please submitted through web at
https://github.com/shuLhan/rescached-go/issues.


== AUTHOR

+rescached+ is developed by Shulhan (ms@kilabit.info).


== LICENSE

Copyright 2018, M. Shulhan (ms@kilabit.info).
All rights reserved.

Use of this source code is governed by a BSD-style license that can be found
in the LICENSE file.


== LINKS

- Source code repository: https://github.com/shuLhan/rescached-go
- RFC 1035: https://tools.ietf.org/html/rfc1035
- Improving DNS Privacy in Firefox: https://blog.nightly.mozilla.org/2018/06/01/improving-dns-privacy-in-firefox/


== SEE ALSO

*rescached.cfg*(5)