Setup and Administration¶
While the Quick Start instructions will get you exploring the Tangelo examples in just two commands, Tangelo has a rich set of configuration options that can be used to administer Tangelo effectively. This page will discuss configuration and deployment strategies, including suggestions for best practices.
Configuring and Launching Tangelo¶
The simplest way to launch a Tangelo server is to use this command:
tangelo
Tangelo’s runtime behaviors are specified via configuration file and command line options. Tangelo configuration files are YAML files representing a key-value store (“associative array” in YAML jargon) at the top level. Each options is specified as a key-value pair: the line starts with the name of the key, then a colon followed by a space, and then the value.
The example configuration found at
/usr/share/tangelo/conf/tangelo.local.conf
reads something like the
following:
hostname: 0.0.0.0
port: 8080
This minimal configuration file specifies that Tangelo should listen on all
interfaces for connections on port 8080. By contrast, tangelo.conf.global
looks like this:
hostname: 0.0.0.0
port: 80
user: nobody
group: nobody
This configuration file is meant for the case when Tangelo is to be installed as
a system-level service. It will run on port 80 (the standard port for an HTTP
server) and, though it will need to be started with superuser privileges, it
will drop those privleges to run as user nobody
in group nobody
to
prevent damage to the system should the process be, e.g., hijacked by an
attacker.
To run Tangelo using a particular configuration file, tangelo
can be invoked
with the -c
or --config
option:
tangelo -c ~/myconfig.yaml
When the flag is omitted, Tangelo will use default values for all configuration options (see Configuration Options below).
Finally, all configuration options can also be specified on the command line. This has the effect of overriding whatever value may be set in the specified configuration file. This can be useful for, e.g., using a single configuration file for multiple Tangelo instances, but varying the port number.
Configuration Options¶
The following tables, organized by section title, show what fields can be included in the configuration file, what they mean, and their default values if left unspecified.
Option | Meaning | Default value |
---|---|---|
hostname | The hostname interface on which to listen for connections | localhost |
port | The port number on which to listen for connections | 8080 |
root | The path to the directory to be served by Tangelo as the web root | /usr/share/tangelo/www [1] |
drop-privileges | Whether to drop privileges when started as the superuser | True |
sessions | Wehther to enable server-side session tracking | True |
user | The user account to drop privileges to | nobody [2] |
group | The user group to drop privileges to | nobody [2] |
access-auth | Whether to protect directories containing a .htaccess file |
True |
key | The path to the SSL key | None [3] [4] |
cert | The path to the SSL certificate | None [3] [4] |
Footnotes
[1] | The first component of this path may vary by platform. Technically,
the path begins with the Python value stored in sys.prefix ; in a Unix
system, this value is /usr, yielding the default path shown here. |
[2] | (1, 2) Your Unix system may already have a user named “nobody” which has the least possible level of permissions. The theory is that system daemons can be run as this user, limiting the damage a rogue process can do. However, if multiple daemons are run this way, any rogue daemon can theoretically gain control of the others. Therefore, the recommendation is to create a new user named “tangelo”, that also has minimal permissions, but is only used to run Tangelo in privilege drop mode. |
[3] | (1, 2) You must also specify both key and cert to serve content over https. |
[4] | (1, 2) That is to say, the option is simply unset by default, the equivalent of not mentioning the option at all in a configuration file. |
Administering a Tangelo Installation¶
Administering Tangelo on a particular system requires making some decisions about how Tangelo ought to behave, then implementing those decisions in a configuration file.
For example, as the system administrator you might create a directory on the web
server machine at /srv/tangelo
which would serve as the web root, containing
the website front page and supporting materials.
You should then prepare a plugin configuration file that, at the very least, activates the Tangelo plugin:
enabled: true
path: /usr/share/tangelo/plugins/tangelo
This file can be saved to /etc/tangelo/plugin.conf
.
It remains to configure Tangelo itself. The hostname should reflect the desired external identity of the Tangelo server - perhaps excelsior.starfleet.mil. As this is a “global” deployment, we want to listen on port 80 for connections. Since we will need to start Tangelo as root (to gain access to the low-numbered ports), we should also specify a user and group to drop privileges to: these can be the specially created user and group tangelo.
The corresponding configuration file might look like this:
# Network options.
hostname: excelsior.starfleet.mil
port: 80
# Privilege drop options.
user: tangelo
group: tangelo
# Runtime resources.
root: /srv/tangelo
This file should be saved to /etc/tangelo.conf
, and then Tangelo can be
launched with a command like tangelo -c /etc/tangelo.conf
(the sudo
may
be necessary to allow for port 80 to be bound).
Running Tangelo as a System Service¶
Tangelo does not include any mechanisms to self-daemonize, instead running in,
e.g., a terminal, putting all logging output on stdout
, and offering no
facilities to track multiple instances by PID, etc. However, the Tangelo
package includes some scripts and configurations for various system service
managers. This section contains some instructions on working with the supported
managers. If you would like a different system supported, send a message to
tangelo-users@public.kitware.com or fork the GitHub repository and send a pull request.
systemd¶
systemd is a Linux service manager daemon for which a unit file corresponds
to each service. Tangelo supplies such a unit file, along with supporting
scripts, at /usr/share/tangelo/daemon/systemd
. To install Tangelo as a
service, the files in this directory need to be copied or symlinked to a location
from which systemd can access them. An example follows, though your particular
system may require some changes from what is shown here; see the systemd
documentation for more
information.
Go to the place where systemd unit files are installed:
cd /usr/lib/systemd/system
Place an appropriate symlink there:
sudo ln -s /usr/share/tangelo/daemon/systemd/system/tangelo@.service
Go to the systemd auxiliary scripts directory:
cd ../scripts
Install a symlink to the launcher script:
sudo ln -s /usr/share/tangelo/daemon/systemd/scripts/launch-tangelo.sh
Now you will be able to control Tangelo via the systemctl
command.
Note that the unit file defines Tangelo as an instantiated service, meaning
that multiple Tangelo instances can be launched independently by specifying an
instantiation name. For example:
sudo systemctl start tangelo@localhost:8080
will launch Tangelo to run on the localhost interface, on port 8080. The way
this works is that systemctl
takes the instantiation name (i.e., all the
text after the @
symbol - localhost:8080) and passes it to
launch-tangelo.sh
. It in turn parses the hostname (localhost) and port
number (8080) from the name, then launches Tangelo using whatever
configuration file is found at /etc/tangelo.conf
, but overriding the
hostname and port with those parsed from the name. This allows for a unique
name for each Tangelo instance that corresponds to its unique web interface.
A Note on Version Numbers¶
Tangelo uses semantic versioning for its version numbers, meaning that each release’s version number establishes a promise about the levels of functionality and backwards compatibility present in that release. Tangelo’s version numbers come in two forms: x.y and x.y.z. x is a major version number, y is a minor version number, and z is a patch level.
Following the semantic versioning approach, major versions represent a stable API for the software as a whole. If the major version number is incremented, it means you can expect a discontinuity in backwards compatibility. That is to say, a setup that works for, e.g., version 1.3 will work for versions 1.4, 1.5, and 1.10, but should not be expected to work with version 2.0.
The minor versions indicate new features or functionality added to the previous version. So, version 1.1 can be expected to contain some feature not found in version 1.0, but backwards compatibility is ensured.
The patch level is incremented when a bug fix or other correction to the software occurs.
Major version 0 is special: essentially, there are no guarantees about compatibility in the 0.y series. The stability of APIs and behaviors begins with version 1.0.
In addition to the standard semantic versioning practices, Tangelo also tags the current version number with “dev” in the Git repository, resulting in version numbers like “1.1dev” for the Tangelo package that is built from source. The release protocol deletes this tag from the version number before uploading a package to the Python Package Index.
The tangelo.requireCompatibleVersion()
function returns a boolean
expressing whether the version number passed to it is compatible with Tangelo’s
current version.