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.