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Inclusion of best practices for packaging database applications in Debian policy




Hi Debian developers,

This e-mail is meant for maintainers of applications that use databases
and for those of you that are interested in how packages should handle
those.

In bug 845255¹ I started the discussion for inclusion of the "best
practices for packaging database applications" in the Debian policy.
These practices were written down by Sean Finney more than 12 years ago
after discussion that started on this list (see links in the
documentation). These best practices have always been part of the
dbconfig-common package and are available on debian.org/doc² for a year
now. After consulting the audience of my talk at Debconf, I think these
practices (or an altered form if required after discussion) should be
part of the Debian policy. In the bug it is said I should ask for
seconds of this proposal from database application maintainers, which I
am hereby seeking.

Please follow-up in the policy bug¹ (reply-to set).

For ease of the readers, the full text is given below.

Paul

¹ https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=845255
² https://www.debian.org/doc/manuals/dbapp-policy/ch-dbapps.html


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Best practices for packaging database applications
Chapter 1 - Database Applications

1.1 Scope

In this document a "database application" is any program that relies on
some form of data storage outside the scope of the program's execution.
This is primarily intended to encompass applications which rely on a
relational database server or their own persistent storage mechanism,
though effectively is a much larger set of applications. In the future
this scope may have to be narrowed to avoid ambiguity and be more
effective as a policy.

1.2 Terminology

For the purposes of this document, there are two types of databases:
persistent and cached.

Persistent databases contain data that can not be entirely reconstituted
in the case that the database is removed. Also included are databases
that if removed would cause serious denial of service (making a system
unstable/unusable) or security concerns. Applications using this
category of databases are the primary focus of this document. Examples:

    relational database servers providing storage to other applications.

    web applications using a relational database

    openldap's slapd databases

    rrd files containing accumulated/historical data.

Cached databases are a specific group of databases which upon their
removal could be sufficiently regenerated, and could be removed without
causing serious denial of service or security concerns. Examples include:

    debconf responses

    locate database

    caching nameserver data

    apt's list of available packages

1.3 Placement of databases

Both persistent and cached databases fall under already defined
guidelines in the FHS; persistent data must be placed under
/var/lib/packagename, and cached data under /var/cache/packagename,
respectively [1]. The remainder of this document primarily addresses the
former.

1.4 Installation related issues

The following descriptions are divided into different parts, based on
the action being performed. For each process, the acceptable behavior of
database application packages is outlined.

1.4.1 Automatic Database Configuration/Prompting

It must always be assumed that the local admin knows more than any
automated system. He/She must be given the ability to opt out of any
"assistance" on the part of the package maintainer. Packages providing
any such automated assistance may do so by default if and only if the
opt-out debconf prompt is equal to or greater than priority high. With
this in mind, directions for manually installing (and upgrading if
relevant) the database must be included in the documentation for the
package.

1.4.2 Database Installation

For packages providing automated assistance, database
installation/configuration should be considered as part of the package
installation process. A failure to install a database should be
considered a failure to install the package and should result in an
error value returned by the relevant maintainer script. Packages may
provide a "try again" option to re-attempt configuration. Any such "try
again" features here or elsewhere mentioned in this document must have a
default negative response value, otherwise infinite loops could occur
for noninteractive installs.

To properly handle package reinstallation and reconfiguration, any
automated assistance must allow for a package to be reinstalled at the
same version without removing or overwriting existing application data.
Package reconfiguration may do so.

1.4.3 Database Upgrading

Occasionally a new upstream version of an application will require
modifications to be made to the application's underlying database. If an
automated system is to assist in such an upgrade, it should be
considered as a part of the package upgrade process; failure to upgrade
the database should be considered a failure to upgrade the package. This
is the only way to safely guarantee the chance to reattempt the upgrade
with respect to the underlying database.

Furthermore, any automated system that makes modifications to a database
during upgrade must provide the ability to back-up the database before
proceeding. Packages may perform such backups automatically, or prompt
the admin via debconf. Failure to back up the database should also be
considered a failure in the upgrade process of the whole package. As in
the case of installation, automated assistance may provide a "try-again"
feature to re-attempt the upgrade, but ultimately in the case of failure
should cause a non-zero exit value to be returned to dpkg.

Note: if the database in question supports transactional operations, it
is recommended to do so.

1.4.4 Database Removal

A package should consider databases in a spirit similar to configuration
files or log files; they are something to which the administrator may
have some need even when the software that created it is no longer present.

Packages may provide support for removing underlying databases, but it
is highly recommended that the administrator is prompted with a chance
to preserve the data before doing so.

1.5 Build-time and run-time tools

While not essential, a set of common tools for packaging and configuring
these applications can make the life of the maintainer as well as the
administrator much easier.

1.5.1 dbconfig-common

dbconfig-common is a common framework for packaging database
applications. More information can be found in the dbconfig-common
section of the Debian documention for maintainers, or under
/usr/share/doc/dbconfig-common.

1.6 Related threads/discussions

    RFC: best practice creating database

    RFC: common database policy/infrastracture

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Best practices for packaging database applications
Sean Finney




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