PEP: 381 Title: Mirroring infrastructure for PyPI Version: $Revision$ Last-Modified: $Date$ Author: Tarek Ziadé Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 21-March-2009 Python-Version: N.A. Post-History: Abstract ======== This PEP describes a mirroring infrastructure for PyPI. Rationale ========= PyPI is hosting over 4000 projects and is used on a daily basis by people to build applications. Especially systems like `easy_install` and `zc.buildout` make intensive usage of PyPI. For people making intensive use of PyPI, it can act as a single point of failure. People have started to set up some mirrors, both private and public. Those mirrors are active mirrors, which means that they are browsing PyPI to get synced. In order to make the system more reliable, this PEP describes: - the mirror listing and registering at PyPI - the pages a public mirror should maintain. These pages will be used by PyPI, in order to get hit counts and the last modified date. - how a mirror should synchronize with PyPI - how a client can implement a fail-over mechanism - a contact form for Package maintainers Mirror listing and registering ============================== A new text page will be added at http://pypi.python.org/mirrors that can be browsed like the simple index. This page gives a list of the mirrors through a list of links. These links are the URL of the simple index of each mirror. The page will look like this:: # PyPI mirrors # # If you want to register a new mirror, send an email # to the catalog-SIG@python.org with: # # - The urls of your mirror: # - the root of the server # - the index page # - the last modified page # - the local stats page # - the global stats page # - the mirrors page # # - The name and email of the maintainer. # # The registering is done manually and to become a # mirror, you need to strictly follow the mirror protocol # described here: # # http://wiki.python.org/PEP_374 # # root,index,last-modified,local-stats,stats,mirrors http://example.com/pypi,index,last-modified,local-stats,stats,mirrors http://example2.com/pypi,index,last-modified,local-stats,stats,mirrors When a mirror is proposed on the mailing list, it is manually added in the mirror list in the PyPI application after it has been checked to be compliant with the mirroring rules. The mirror list page is a simple text page that can be browsed by any tool that wants to get a list of registered mirrors. Other package indexes that are not mirrors of PyPI are not added in the mirror list in PyPI, although they can provide themselve the same mirroring list mechanism for their own mirrors. Special pages a mirror needs to provide ======================================= A mirror needs to provide four pages, beside the index one: - last-modified - local-stats - stats - mirrors Last modified date :::::::::::::::::: CPAN uses a freshness date system where the mirror's last synchronisation date is made available. For PyPI, each mirror needs to maintain a URL with simple text content that represents the last synchronisation date the mirror maintains. The date is provided in GMT time, using the ISO 8601 format (see http://en.wikipedia.org/wiki/ISO_8601). Each mirror will be responsible to maintain its last modified date. Conventionally, this page should be reachable at: `/last-modified`. Local statistics :::::::::::::::: Each mirror is responsible to count all the downloads that where done via it. This is used by PyPI to sum up all downloads, to be able to display the grand total. These statistics are in CSV-like form, with a header in the first line. It needs to obey PEP 305 [#pep305]_. Basically, it should be readable by Python's `csv` module. The fields in this file are: - package: the distutils id of the package. - filename: the filename that has been downloaded. - useragent: the User-Agent of the client that has downloaded the package. - count: the number of downloads. The content will look like this:: # package,filename,useragent,count zc.buildout,zc.buildout-1.6.0.tgz,MyAgent,142 ... The counting starts the day the mirror is launched, and there is one file per day, compressed using the `bzip2` format. Each file is named like the day. For example `2008-11-06.bz2` is the file for the 6th of November 2008. They are then provided in a folder called `days`. For example: - /local-stats/days/2008-11-06.bz2 - /local-stats/days/2008-11-07.bz2 - /local-stats/days/2008-11-08.bz2 Conventionally the name should be `local-stats`, but it can be any name provided when the mirror is registered. Statistics page ::::::::::::::: PyPI and each mirror are responsible to provide the grand total page at `/stats`. This page is calculated daily by PyPI, by reading all mirrors' local stats and summing them. Therefore the mirrors should not try to rebuild this stat page but simply get the one on PyPI during each synchronization. It has the same structure as `local-stats` but also provides counts for months. Examples: - /stats/days/2008-11-06.bz2 - /stats/days/2008-11-07.bz2 - /stats/days/2008-11-08.bz2 - /stats/months/2008-11.bz2 - /stats/months/2008-10.bz2 Conventionally the name should be `stats`, but it can be any name provided when the mirror is registered. Mirrors listing page :::::::::::::::::::: Like `/stats`, each mirror should get and provide a copy of the `/mirrors` page. Conventionally the name should be `mirrors`, but it can be any name provided when the mirror is registered. How a mirror should synchronize with PyPI ========================================= A mirroring protocol called `Simple Index` was described and implemented by Martin v. Loewis and Jim Fulton, based on how `easy_install` works. This section synthesizes it and gives a few relevant links, plus a small part about `User-Agent`. The mirroring protocol :::::::::::::::::::::: XXX Need to describe the protocol here. The zc.pypimirror package [#zcpkg]_ provides an application that respects this protocol to browse PyPI. User-agent request header ::::::::::::::::::::::::: In order to be able to differentiate actions taken by clients over PyPI, a specific user agent name should be provided by all mirroring softwares. This is also true for all clients like: - `zc.buildout `_ - `setuptools `_ - `pip `_ - etc. XXX user agent registering mechanism at PyPI ? How a client can use PyPI and its mirrors ::::::::::::::::::::::::::::::::::::::::: Clients that are browsing PyPI should be able to use alternative mirrors, by reading the `/mirrors` page at PyPI. The clients so far that could use this mechanism: - setuptools - zc.buildout (through setuptools) - pip Fail-over mechanism ::::::::::::::::::: Clients that are browsing PyPI should be able to use a fail-over mechanism when PyPI or the used mirror is not responding. This can be done by parsing the `/mirrors` page of PyPI or the one located on any PyPI mirror. It is up to the client to decide wich mirror should be used, maybe by looking at its geographical location and its responsivness. This PEP does not describe how this fail-over mechanism should work, but it is strongly encouraged that the clients try to use the nearest mirror. The clients so far that could use this mechanism: - setuptools - zc.buildout (through setuptools) - pip Extra package indexes ::::::::::::::::::::: It is obvious that some packages will not be uploaded to PyPI, whether because they are private or whether because the project maintainer runs his own server where people might get the project package. However, it is strongly encouraged that a public package index follows PyPI and Distutils protocols. In other words, the `register` and `upload` command should be compatible with any package index server out there. Softwares that are compatible with PyPI and Distutils so far: - `PloneSoftwareCenter `_ wich is used to run plone.org products section. - `EggBasket `_ **An extra package index is not a mirror of PyPI, but can have some mirrors itself.** Merging several indexes ::::::::::::::::::::::: When a client needs to get some packages from several distinct indexes, it should be able to use each one of them as a potential source of packages. Different indexes should be defined as a sorted list for the client to look for a package. Each independant index can of course provide a list of its mirrors, if the `/mirrors` page is available. That permits all combinations at client level, for a reliable packaging system with all levels of privacy. It is up the client to deal with the merging. References ========== .. [#pep305] http://www.python.org/dev/peps/pep-0305/#id19 .. [#zcpkg] http://pypi.python.org/pypi/z3c.pypimirror Copyright ========= This document has been placed in the public domain. .. 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