= README

Simple and fast configuration management (safcm) is written in Go and licensed
under GPLv3+. It is:

- *simple*: to use and implement, obvious concepts and less bugs
- *fast*: to learn and to use, quickly apply new configurations to your hosts
- *configuration management*: sync files, packages, services and run commands
  on remote hosts

The goal is that even inexperienced users (with safcm or configuration
management in general) should be able to apply configuration with safcm
quickly. This means all key concepts of safcm must be easy to grasp and for
each task there should be one obvious way.

It can also be read as "saf(e) configuration management" as it combines
simplicity and safety in the following principles:

- *fail fast*: catch (user) errors as soon as possible; host configuration
  (including templates) is evaluated locally to prevent partial configuration;
  errors immediately abort the synchronization
- *remote hosts are untrusted*: clear security boundary between local and
  remote host; data used from remote hosts is marked tainted (detected
  groups); all output from remote hosts is escaped to prevent terminal
  injection attacks; each host only receives its own configuration and no data
  from other hosts
- *safety and security*: create files with "write to temporary file", "sync",
  "rename", "sync directory" for atomicity and durability; implemented in a
  memory safe language and using a simple synchronization protocol to prevent
  attacks on the local host; guard against symlink and other TOCTOU attacks;
  extensive test suite


== Overview

This section describes the general concepts, behavior and terminology of
safcm.

Safcm _synchronizes_ _files_, _packages_, _services_ and _commands_ to remote
_hosts_. All hosts are explicitly configured. Hosts can be put into _groups_
to apply the same configuration to multiple hosts. The host itself is also
considered a group for host-specific configuration. In addition to manual
group assignment _detected groups_ assign hosts to groups depending on the
output of custom commands on the remote host. The _configuration_ for a group
contains the files, packages, services and commands which should be applied to
all hosts which are members of this group.

The configuration of all managed hosts is stored in a directory on the local
host. Safcm uses https://yaml.org/[YAML] for all configuration files. Strict
type checks prevent potential pitfalls due to the complex YAML syntax. Tasks
like copying a file require no explicit configuration.

Files (regular files and symbolic links) and directories, including
permissions, user/group and content are kept in a regular filesystem tree on
the local host. Files can use _templates_ for dynamic content depending on the
host or its groups. Each path can have _trigger_ commands which are executed
when the path itself or any sub-paths are modified during synchronization.
Packages are package names of the remote operating system. Services are
service names of the remote operating system. Commands are shell commands
passed to `/bin/sh`.

When files with the same path are present in multiple groups of a host, an
explicit _group priority_ must be configured to resolve the conflict.
Conflicts do not apply to packages and services which are simply merged from
all groups. Commands are appended so that the same command can be executed
multiple times.

To sync the configuration to a remote host, the local `safcm` binary connects
to it via `ssh`. It then copies a _remote helper_ binary to `/tmp` on the
remote host to perform the actual sync later. If the remote helper is already
present, has the proper checksum, permissions and user/group then the copying
step is skipped. `safcm` then queries the remote host for information,
including operating system, architecture and detected groups. With all
relevant data collected, it assigns the host to its groups, evaluates the
configuration including templates and finally sends the new configuration to
the remote helper which then applies it to the remote host.

The synchronization happens in the following order which cannot be changed:

. Collect information from remote helper including detected groups
. Build configuration for the host and send it to the remote helper
. Apply the configuration using the remote helper
.. Synchronize files
.. Install packages
.. Enable/Start services
.. Run triggers
.. Run commands

After the synchronization is complete (or on the first error) the applied
changes are displayed. Multiple hosts are synchronized in parallel.


== Limitations & Gotchas

Besides some obvious limitations due to the simplicity of safcm there are a
few issues the user should be aware of. Some of these might get fixed in the
future, others are due to the design of safcm.

- Commands are executed with `/bin/sh -c` on the remote host which might leak
  sensitive information to other users via the command line (unless `/proc` is
  mounted with `hidepid=` on GNU/Linux systems). Store sensitive data in a
  file and execute or source it as a workaround.

- Permissions of existing files and directories will be overwritten with the
  default (root/root or root/wheel, 0644 for files, 0755 for directories)
  unless manually configured via `permissions.yaml`. This includes important
  paths like `/root` which often have strict permissions by default, so
  carefully check the output for unwanted changes.

- The full file content of all files is sent to the remote during
  synchronization. This makes it impractical to synchronize large files with
  safcm. Since most configuration files are small this shouldn't be an issue
  for common scenarios.

- Quoted strings in the output are quoted using Go's `%q` format string. The
  result is similar -- but not identical -- to quoted strings in regular shell
  scripts which can be confusing.

- Permissions of symlinks are ignored on BSD systems. They are always shown to
  have `0777` as permissions even though the current umask controls the actual
  permissions when creating new symlinks. Existing symlinks with different
  permissions are not updated. Most BSDs ignore the permissions when following
  symlinks which should reduce the impact of this limitation.


== Requirements

- to build the `safcm` binary and remote helper:
  * Go >= 1.16 (for `go:embed`, `io/fs`)
  * GNU make

- local host:
  * Go support for architecture and operating system, see the "$GOOS and
    $GOARCH" section in the official
    https://golang.org/doc/install/source#environment[Go installation guide]

- *remote hosts*:
  * Go support for architecture and operating system
  * Supported operating system:
    ** GNU/Linux with common commands (`uname`, `id`, `stat`, `sha512sum`,
       `cat`, `mktemp`, `rm`, `ln`, `chmod`)
    ** FreeBSD (same commands, but uses `sha512`)
    ** OpenBSD (same commands, but uses `sha512`)
  * SSH server
  * to install packages:
    ** `apt-get` (Debian or derivative)
  * to sync services:
    ** `systemd`

Adding support for other operating systems (e.g. BSDs) or distributions
including package managers (e.g. Arch, Gentoo) is easy. Please send patches.

At the moment the remote helper is built for the following operating systems
($GOOS) and architectures ($GOARCH). To add more architectures simply edit
`cmd/safcm-remote/build.sh`.

    - freebsd: amd64
    - linux: amd64, armv7
    - openbsd: amd64


== Authors

Written by Simon Ruderich <simon@ruderich.org>.


== License

This program is licensed under GPL version 3 or later.

Copyright (C) 2021-2024  Simon Ruderich

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
