Openstack Swift is a mass scale object storage, coded in pure Python. It has code organized in following components:
- account
- container
- proxy
- obj
- common
Things to remember
- This is a single node, very first look at Swift code.
- Code: https://github.com/openstack/swift
- Installation: Use SAIO (Swift All In One). It is not complete, I guess. I did the following:
- Do all at: http://docs.openstack.org/developer/swift/development_saio.html
- $ sudo apt-get install swift-proxy memcached
- Don’t forget: Git clone the Swift code and build swift client and swift
- All components in swift are WSGI based web servers. You will find GET, PUT, POST, HEAD, DELETE implemented here. There are good points to start understanding code.
- An object has a storage path. This path is combination of account, container and object-name. Consider this path as a key.
- Each path is unique. Using the storage path, an object can be retrieved from the cluster.
- Ring is an outsider stuff. Don’t worry about it in the beginning.
- obj: Code for storage server.
- It has code to write/ read objects on local disk. Start from “server.py”.
- container: A catalog of stored objects.
- It is stored as a SQLite database. Look at “server.py”
- account: Code for account.
- Yet to take a close look.
- proxy: The main component that accepts requests from outside world.
- It has three controllers under ./controller/: obj, account and container.
- Each of these are WSGI web services and would call their respective handlers.
- Each request to proxy might involve execution of multiple operations. e.g. a GET request needs a HEAD request to container server and followed by a GET request to object server. The former confirms existence of the object, the latter fetches it.
- Useful files: All of’em.
- server.py: Base Proxy server
- ./controller/account: Calls account server
- ./controller/container: Calls container server
- ./controller/obj: Calls object server
- Debug logs: /var/log/syslog has logs for all mentioned components
