About Sandcats.io
Sandcats.io is a free-of-cost dynamic DNS service run by the Sandstorm development team. In a nutshell:
-
Sandstorm users can have a free domain name of the form
example.sandcats.io
. -
Sandstorm can automatically set up that domain, including a valid HTTPS certificate for it.
-
It's an official part of Sandstorm and we recommend people use it!
In more detail:
-
Users host their own servers. A hostname like
example.sandcats.io
points at the IP address of someone's server, and that server holds its own private keys. -
It assumes your server should be reachable from the global Internet.
-
It's an optional service. Keep reading this page to learn how to stop using it.
-
It points at your server's public (globally routable) IP address, which it auto-detects. Read elsewhere about setting up Sandstorm to use an internal IP address.
The purpose is to help people who run their own server have a working hostname and HTTPS (TLS/SSL) certificate without having to think hard about the domain name system or public key infrastructure.
Features
Sandcats is integrated into the Sandstorm installer so that when you install Sandstorm, you get working DNS, including wildcard DNS, as well as working HTTPS for the main Sandstorm interface.
The Sandcats backend is free, open source software under the Apache License 2.0; you can view and participate in the project.
The Sandcats DNS service provides 60-second latency for IP address updates via a custom UDP protocol to detect address changes. To achieve this low latency, when Sandcats integration is enabled, your Sandstorm server sends a UDP ping message to the central Sandcats service every 60 seconds.
Administering your sandcats.io subdomain
Finding debugging information
By default, Sandstorm stores a log in a text file at /opt/sandstorm/var/log/sandstorm.log
. You can
read it by running this command:
sudo less /opt/sandstorm/var/log/sandstorm.log
This launches a tool called less
; for help using less
, read this
tutorial.
Disabling the sandcats service
If your Sandstorm server used to use sandcats.io
but you want to transition to
your own domain name (with wildcard DNS), you can disable the sandcats-related code
in your Sandstorm install.
To do that, open your /opt/sandstorm/sandstorm.conf
file in a text editor and notice this line:
SANDCATS_BASE_DOMAIN=sandcats.io
Remove that line entirely, then save and quit your editor. Run sudo service sandstorm restart
to
cause Sandstorm to notice your changes to its configuration file.
That will disable the sandcats-related functionality in your Sandstorm server on your system. This means your domain will stop automatically updating its IP address.
Note that this does not delete any domains you registered. That's OK with us; from our perspective, there's no need to email us to delete your domain.
Re-installing Sandstorm and keeping your sandcats domain
If you have already registered a domain like example.sandcats.io
as part of installing Sandstorm,
but you find yourself doing a fresh install of Sandstorm, you can use our email-based recovery
system.
You won't need any files from the old Sandstorm install. Instead, run the Sandstorm install script
(which we call install.sh
) on a new server; follow the prompts to recover a domain by typing
help
at the Sandcats prompts.
Overview. This process will:
-
Ask you what
sandcats.io
subdomain you use. -
Send you an email with a short-term token.
-
Ask you for the token, then pass it to the sandcats.io service.
The install will continue and your new Sandstorm install will be bound to example.sandcats.io
.
Full details for those who are curious.
-
When you run the
install.sh
script, if you choose mode1
for a full server, and you sayyes
to the defaults,install.sh
prepares to enablesandcats.io
(even if you end up not using thesandcats.io
service). -
Specifically,
install.sh
looks for an existing client certificate on your system in/opt/sandstorm/var/sandcats/id_rsa.private.combined
.sandcats.io
uses client certificates to identify a Sandstorm server as controlling a specific domain likeexample.sandcats.io
. Ifinstall.sh
does not find one, it generates one usingopenssl
. -
install.sh
asks via the console what sandcats domain you want to register. At this point, you can typehelp
. This changes the question -install.sh
now asks what domain you want to recover. Provide your sandcats hostname. -
install.sh
then usescurl
to asksandcats.io
to send an email to the address that you provided when first registering the domain. The email contains a small bit of text that serves as a one-time-use recovery token. -
install.sh
waits for you to receive the email and asks via the console for your recovery token. -
install.sh
sends that recovery token tosandcats.io
usingcurl
, while also providing the client certificate currently on your system (/opt/sandstorm/var/sandcats
). If the recovery token matches what the server expects, then the server updates your user registration to trust the client certificate on your system.
Manually moving sandcats client certificates to a new Sandstorm install
If you prefer, you can move your sandcats.io
credentials to a new Sandstorm install without
running the install.sh
script. We call that file-based recovery. Here are the steps.
-
Find your three three
id_rsa
certificate files (usually/opt/sandstorm/var/sandcats
) and keep them safe somewhere. Also keep a copy of/opt/sandstorm/var/sandcats/https
if it exists. -
Do a new Sandstorm install, presumably on a new server somewhere. It will install to
/opt/sandstorm
. You should choose a non-sandcats.io host name during this process, such as using literallyexample.com
. -
Copy those three
id_rsa
certificate files from the old server to the new server's Sandcats directory,/opt/sandstorm/var/sandcats
. Do the same for/opt/sandstorm/var/sandcats/https
if you backed it up. -
In your new Sandstorm install, ensure you have your
BASE_URL
andWILDCARD_HOST
set properly. If your sandcats.io subdomain isexample
, then you'll needBASE_URL=example.sandcats.io
andWILDCARD_HOST=*.example.sandcats.io
. Consider copying these values from the old server'ssandstorm.conf
. -
Edit the new server's
sandstorm.conf
to contain this line:SANDCATS_BASE_DOMAIN=sandcats.io
-
Now restart Sandstorm by running
sudo service sandstorm stop ; sudo service sandstorm start
, and wait at least 60 seconds. -
Your DNS hostname should have auto-updated. Check that DNS is working with
nslookup <myname>.sandcats.io
from another machine. This will help eliminate DNS as an issue when trying to access your server.
Diagnosing "Not Authorized" problems
If you see Not Authorized
in your log files, the sandcats.io service is returning HTTP code 403
for at least one request from your server.
One reason this occurs is if you have the wrong id_rsa*
certificate files in
/opt/sandstorm/var/sandcats
. You can fix this problem using the email-based recovery system; for
now, this requires using install.sh
on a throwaway VM. Once your new certificate files are
registered with sandcats.io
, you can move them to whichever server you want using file-based
recovery.
Another reason you might see Not Authorized
in the log files is if your server has run afoul of
sandcats.io's defense in depth against Sandstorm bugs.
In either case, if you need further help, please email support@sandstorm.io!
Terms of service, privacy policy, & contact information
Sandcats.io has the following formal documents:
If you have more questions, or are having trouble, email: