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Table of Contents:

Intro

Historically, all of my Fossil hosting, since 2008, has been on shared hosters via CGI, without any access to dedicated server capabilities. This system represents my first time having access to a full-fledged public-facing server from which to host fossil. This document describes how it is set up and touches on some of the reasons for certain decisions, e.g. the choice of web server.

In short, the server is comprised of:

The choice of OS was primarily one of habit and comfort: Linux is my virtual home since last millennium. The choice of fossil wasn't really a choice at all: it's the reason for setting up this server in the first place. The other choices were made after evaluating several options. This document won't provide an essay on each of those choices but will touch upon them in the relevant sections.

See mailserver.md for how this system's mail server is set up.

Prerequisite Software

This document will not detail the process of installing each piece of software except where it's deemed unusually exotic. The majority of the software it uses is available via the OS-level package repository. In particular, on this system we require:

$ apt install stunnel4 xinetd snapd docker.io

(snapd is required for certbot on Ubuntu.)

We also need a copy of fossil somewhere in the PATH. Make sure to get a recent version, or build it from its trunk, rather than relying on a semi-ancient version provided in the OS's package repositories. See below for instructions on building a static fossil binary via docker.

An Administrative User

The content on this system is owned (in terms of filesystem permission) and administered by a non-root user who has SSH access to the system, as opposed to a system-level user like www-data. That user requires root access via sudo in order to complete the main setup and perform occasional system-level tasks, but administering the web content requires no root access. If the environment is set up such that the content is owned by a user who cannot log in (like www-data) then most administrative tasks will require logging in as root and chown'ing the files to the proper user. When these docs refer to USER, they're referring to the non-root user who manages the site content.

Setup the chroot Jail

All of the public-facing content on this server is hosted under a so-called "chroot jail," which is essentially a directory tree in the filesystem in which the web server locks itself before starting to serve data. This security measure means that if someone manages to find a hole in the web server and gain access to the system via that process, they're limited to non-root access within that one branch of the filesystem. As the chroot jail holds only a bare minimum of system-level files, it's not even possible for an attacker to "sudo" their way out of it.

Debian-based Linux systems have an easy approach to installing full-featured chroot environments, but ours is intentionally as minimal as possible. For those interested in full-featured over minimal, see:

https://www.linode.com/docs/guides/use-chroot-for-testing-on-ubuntu/

The chroot environment was set up via a sequence of shell commands almost identical to the following, noting that (1) they require root access) and (2) USER refers to a non-root user account on whose behalf most of the web content will be managed.

Initial chroot Setup

$ mkdir -p /jail/dev
$ cd /jail/dev
$ mknod null c 1 3 # <-- values are OS-dependent!
$ mknod urandom c 1 9 # <-- values are OS-dependent!
$ chmod 0666 null urandom
$ cd ..
$ mkdir proc
$ chmod 0555 proc
$ mount -t proc /proc proc/
# ^^^^ see below for fstab entry
# ./tmp is required for chrooted fossil writing temp files:
$ mkdir tmp
$ chown USER tmp
$ mkdir .well-known
# ^^^ part of the ACME protocol for SSL cert renewal

The /proc and /tmp filesystems require mounting on each reboot, so add these lines to /etc/fstab:

/proc		/jail/proc	proc	defaults	  0	2
swap		/jail/tmp	tmpfs	defaults,size=500m,uid=USER  0	2

and then:

$ mount /jail/tmp

Static Fossil Binary via Docker

For our minimalistic chroot we need a completely static fossil binary. Though we can ostensibly build a static binary using the --static flag to fossil's configure script, the resulting binary is not truly static on Linux enviroments which use glibc. In order to build a truly static binary on Linux, we need an environment with a different libc. Fortunately, this is really easy to do with Docker.

The initial Docker setup looks like:

$ sudo apt install docker.io
# Add USER to the docker group:
$ sudo usermod -a -G docker USER
# ^^^ logout/login will be necessary for the user
#     to activate their access to that group.

With that in place we can build a static fossil binary. Copy the Dockerfile and build script shown below somewhere convenient, e.g. ~/tmp, cd to that directory, then run that script...

Static Build Wrapper Script

#!/bin/sh
set -e
set -x
docker build -t fossil_static \
       --build-arg cachebust=$(date +%s) \
       "$@" \
       .
docker create --name fossil fossil_static
docker cp fossil:/fossil-src/fossil fossil
strip fossil
ls -la fossil
docker container rm fossil
set +x

cat <<EOF
Now maybe do:
  docker image rm \$(docker image ls | grep -e fossil_static -e alpine | awk '{print $3}')
or:
  docker system prune --force
EOF

Dockerfile

This file must saved as Dockerfile or the above wrapper script must be modified to pass the -f filename flag to docker build.

########################################################################
# Builds a static fossil SCM binary from the latest trunk
# source code.
# Optional --build-arg entries:
#    repoUrl=source repo URL (default=canonical tree)
#    version=tag or version to pull (default=trunk)
#    cachebust=an arbitrary value to invalidate docker's cache
########################################################################

ARG repoUrl=https://fossil-scm.org/home
ARG version=trunk
ARG cachebust=0
# FROM    alpine:edge
# >3.13 breaks stuff unduly:
# https://wiki.alpinelinux.org/wiki/Draft_Release_Notes_for_Alpine_3.14.0#faccessat2
FROM    alpine:3.13

RUN apk update && apk upgrade                  \
    && apk add --no-cache                      \
      curl gcc make tcl musl-dev               \
      openssl-dev zlib-dev openssl-libs-static \
      zlib-static
ARG repoUrl
ARG version
ARG cachebust
RUN curl                                  \
      "${repoUrl}/tarball/fossil-src.tar.gz?name=fossil-src&uuid=${version}"  \
      -o fossil-src.tar.gz                   \
      && tar xf fossil-src.tar.gz            \
      && cd fossil-src                       \
      && ./configure                         \
      --static                               \
      --disable-fusefs                       \
      --json                                 \
      && make

Build the Static Fossil

$ ./build-fossil.sh
...
$ sudo mv fossil /jail/bin/.

Setup SSL Cert via certbot

certbot offers free short-lived SSL certificates and automation to renew them.

This step requires that at least one domain or subdomain has already been mapped to this server's static IP(s) and that resolution of that domain has propagated through the DNS system.

Precisely how to set up certbot is platform-specific but trivial. Simply select the operating environment from:

https://certbot.eff.org/instructions

And walk through the steps. For purposes of this server, when selecting a web server for certbot, the proper choice was "other" (as opposed to Apache or nginx or "hosted").

The certbot process took less than 10 minutes to complete (at a leisurely pace) and ended with output similar to:

Certificate is saved at: /etc/letsencrypt/live/MY-DOMAIN/fullchain.pem
Key is saved at:         /etc/letsencrypt/live/MY-DOMAIN/privkey.pem
This certificate expires on 2022-04-04.
These files will be updated when the certificate renews.
Certbot has set up a scheduled task to automatically renew this
certificate in the background.

We need to remember that /etc/letsencrypt/... path for later. We'll need it for setting up SSL access to the web content.

On this platform that process sets up automation to renew the certificate as needed, so certbot becomes mostly a background detail. A following section explains a couple of scripts we need for managing certbot, but the software those scripts rely on will not be installed until a later step in the setup process.

Althttpd HTTP Server

Despite my being a long-time user of Apache, setting up this server was seen as an opportunity to try out a different web server solution. Apache, nginx, and althttpd were all evaluated, and althttpd was chosen because:

Sidebar: nginx was only "superficially" evaluated, not actually tested. Certainly it would have been a good solution as well.

Sidebar: Another option would have been to use fossil's own embedded HTTP server, which includes SSL support as of January 2022. Though it would have been about 95% sufficient for this task, hosting of certain static content would not have worked as-is in that setup. Namely, though fossil can server static files in a limited capacity, it does not offer any ability to browse static directories, nor auto-select an index.html when given a directory name (on second thought, maybe it can?). althttpd also cannot browse static directories, but the way it supports CGIs makes that easy to to do via small CGI scripts which provide rendering of the contents of such directories.

althttpd is a single-source-file solution which must be downloaded, compiled, and installed:

$ fossil clone https://sqlite.org/althttpd
$ cd althttpd
$ make
$ sudo mv althttpd althttpsd /jail/bin

Adding Websites to althttpd

Althttpd uses the directory specified by its -root DIR argument as its virtual root, but it requires that a separate directory exist for each website. The directory name is a normalized form of the (sub)domain name which is used to access the site, as documented in althttpd's own docs. At a very minimum, it requires a directory named default.website, which is the fallback it uses if it cannot find a directory name matching the one which is used by the client to access the site.

The -root DIR is the virtual root for chroot purposes, but the content root is the *.website directory corresponding to the site being accessed. CGI scripts must have all of their required resources, e.g. binaries and any shared libraries they need, installed under the -root DIR directory.

Setup stunnel4 (for HTTPS access)

Historically, stunnel4 was the go-to solution for wrapping althttpd in a TLS-capable connection. As of January 14, 2022, althttpd can be compiled with built-in TLS support using OpenSSL, making stunnel optional for TLS support.

$ sudo apt install stunnel4
$ sudo emacs /etc/stunnel4/my.conf
pid = /var/run/stunnel4/stunnel.pid

cert = /etc/letsencrypt/live/DOMAINNAME/fullchain.pem
key = /etc/letsencrypt/live/DOMAINNAME/privkey.pem
[https]
accept       = :::443
TIMEOUTclose = 0
exec         = /jail/bin/althttpd
; Remember that some paths here are relative to chroot'd /jail:
execargs     = /jail/bin/althttpd -logfile /log/althttpd.log -root /jail -user USER -https 1

^X^S

$ sudo service stunnel4 restart

As of this writing (Jan 18, 2022), stunnel is no longer deployed on this server.

Optional: Setup xinetd (for HTTP(S) access)

If HTTP access is required or desired, it can be provided by a standalone instance of althttpd or, optionally, via a service like xinetd. For this server xinetd was chosen on the tried-and-true grounds of "a working example was already available."

$ sudo apt install xinetd
$ sudo emacs /etc/xinet.d/http
service http
{
  port = 80
  flags = IPv4
  bind = PUBLIC_IP_V4_ADDRESS_OF_THIS_MACHINE
  socket_type = stream
  wait = no
  user = root
  server = /jail/bin/althttpd
  server_args = -logfile /log/althttpd.log -root /jail -user USER
}

service http
{
  port = 80
  flags = REUSE IPv6
  bind = PUBLIC_IP_V6_ADDRESS_OF_THIS_MACHINE
  socket_type = stream
  wait = no
  user = root
  server = /jail/bin/althttpd
  server_args = -logfile /log/althttpd.log -root /jail -user USER
}

^X^S

$ sudo /etc/init.d/xinetd restart

Note that the -logfile path in the xinetd configuration is relative to /jail, not /.

xinetd can also, as of January 2022, be used to serve HTTPS instances by adding a snippet like this one to the xinetd config file /etc/xinet.d/https:

service https
{
  port = 443
  flags = IPv4
  socket_type = stream
  wait = no
  user = root
  server = /jail/bin/althttpsd
  server_args = -logfile /log/althttpsd.log -root /jail -user USER -cert /path/to/cert.pem -pkey /path/to/key.pem
}

If the certificate file contains both a certificate and a key, the -pkey flag is optional.

Certbot Renewal Hooks

For certbot auto-renewal to work, we need to arrange for HTTP access to the server to be disabled briefly. We can optionally also disable HTTPS but do not need to, as the renewal process requires only HTTP. The following cerbot hook scripts, or equivalents, need be installed by the root user:

root@www4:/etc/letsencrypt/renewal-hooks# cat pre/stop-www.sh
#!/bin/bash
/usr/bin/systemctl stop xinetd

root@www4:/etc/letsencrypt/renewal-hooks# cat post/start-www.sh
#!/bin/bash
/usr/sbin/service stunnel4 restart
/usr/bin/systemctl start xinetd

Make sure they're executable by root.

With those in place, the certbot renewal process should look like:

root@host:~# certbot --dry-run renew 
Saving debug log to /var/log/letsencrypt/letsencrypt.log

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Processing /etc/letsencrypt/renewal/MY-DOMAIN.conf
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Simulating renewal of an existing certificate for MY-DOMAIN

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Congratulations, all simulated renewals succeeded: 
  /etc/letsencrypt/live/MY-DOMAIN/fullchain.pem (success)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Web Root(s)

Althttpd is capable of hosting multiple domains via a single setup but neither requires nor permits separate explicit configurations for each (sub)domain. Instead, it looks for a directory, relative to the one specified for its -root PATH argument, which matches a normalized form of the domain name with an extension of .website. The transformation and naming conventions can be found in the althttpd docs, but for starters we just need to create a single content directory named default.website (the fallback name althttpd looks for if no domain-specific name is found). Whereas Apache requires configuring each so-called virtual host (a.k.a. vhost) separately, althttpd is geared towards servers operated by a single team with identical setups, where a single configuration can apply to any number of hosts.

In short, althttpd's content-serving rules are: if an exact file match is found, it is served as-is unless that file is executable, in which case it is run as a CGI and its output becomes the HTTP response result (so the output must include any HTTP headers and such). If a directory is requested, althttpd looks in that directory for the first one it finds of (home, index.html, index.cgi), where home is typically a CGI script. althttpd does not offer directory-browsing features like Apache's or like FTP servers typically do, but that is easy to add to any given directory using a CGI script.

Fossil Configuration

This section touches on the configuration of the hosted fossil repositories.

Where to Store Repositories

Ideally all hosted repositories are stored outside of space accessible to the web clients. On this server they are all under /jail/museum and are accessed via CGI wrapper scripts in /jail/fossil_wanderinghorse_net.website/r (here). We "could" run fossil in "directory mode," such that it would list out all repository files from a given directory, but i prefer to have the option to configure each repository separately, as well as "hide" some repositories from common view, and one CGI script per repository, plus an index page listing them, provides that level of flexibility. Directory mode also has the disadvantage of needing to open each repository on every HTTP request in order to pull out its name and description, which would be quite expensive for this server (which has more than 60 repositories).

Sending Notifications from Fossil Repositories

All repositories on this server have the following configuration option in common:

It is important that /jail/notifications and all files in it are writable by the user named in the althttpd -user USER flag. On this system that looks something like:

$ ls -la notifications
total 104
drwsrwx---  2 www-data www-data  4096 Jan 15 16:23 .
drwsrwxr-x 15 root     www-data  4096 Jan 16 05:42 ..
-rw-rw----  1 www-data www-data  8192 Jan 15 12:23 repos.db
-rw-rw----  1 www-data www-data 32768 Jan 17 05:59 repos.db-shm
-rw-rw----  1 www-data www-data 53592 Jan 16 15:58 repos.db-wal

(The www-data user is the one althttpd's running as.)

With that in place, all notifications for all repositories will be added to that db file. Once email is up and running (see mailserver.md for how this server does it), the notifications can be polled and mailed out via a script such as this one:

#!/usr/bin/tclsh

set POLLING_INTERVAL 60000   ;
set DBFILE /jail/notifications/repos.db
set PIPE "/usr/sbin/sendmail -ti"

package require sqlite3
sqlite3 db $DBFILE
db timeout 5000
catch {db eval {PRAGMA journal_mode=WAL}}
db eval {
  CREATE TABLE IF NOT EXISTS email(
    emailid INTEGER PRIMARY KEY,
    msg TXT
  );
}
while {1} {
  db transaction immediate {
    set n 0
    db eval {SELECT msg FROM email} {
      set pipe $PIPE
      if {[regexp {\nFrom:[^\n]*<([^>]+)>} $msg all addr]} {
        append pipe " -f $addr"
      }
      set out [open |$pipe w]
      puts -nonewline $out $msg
      flush $out
      close $out
      incr n
    }
    if {$n>0} {
      db eval {DELETE FROM email}
    }
  }
  after $POLLING_INTERVAL
}

That script runs forever, so should be started in the background using a system service or a cron job. On Linux systems crontab supports a run-time of @reboot to start tasks at system boot, so something like this will do in a pinch:

@reboot sleep 30 && /jail/bin/send-fossil-notifications.tcl

On this particular system we require an intermediary script to start that with:

$ cat send-fossil-notifications.sh
#!/bin/sh
# Workaround to start send-fossil-notifications.tcl without
# my local LD_LIBRARY_PATH's incompatible copy of libsqlite3
# getting in the way.
LD_LIBRARY_PATH=
export LD_LIBRARY_PATH
pid=`pgrep -f send-fossil-notifications`
#If pgrep isn't available (e.g. in busybox):
#pid=`ps -ef | grep send-fossil-notifications.tcl | grep -v grep | awk '{print $1}'`
#^^^^ noting that in busybox the PID is field $1 and in /bin/ps it's $2!
if test x != "x$pid"; then
    kill -9 $pid
fi
exec nohup /jail/bin/send-fossil-notifications.tcl >/dev/null 1>&2 &

Open Issues

Currently none :-D.

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Fossil 2.26 [426dd8d352] 2024-12-12 04:49:40
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