ATOL: Load Balancing
Marek Grac xgrac@fi.muni.cz
Red Hat Czech s.r.o. / Faculty of Informatics, Masaryk University
Advanced Topics of Linux Administration
Marek Grác xgrac@fi.muni.cz        ATOL: Load Balancing
Introduction to load-balancing
► Technique to distribute workload across several computers
► Increase reliability through redundancy
► Application based solutions
► General solutions based on Linux Virtual Server
ipvsadm + pulse / piranha (Red Hat) ipvsadm + ldirectord (Novell)
► General solutions based on DNS (round robin)
► Solutions based on specified network protocol
Marek Grác xgrac@fi.muni.cz        ATOL: Load Balancing
gp - = = ^)c^o
Application based solutions
► Application is written with load-balancing as a feature
► Usually based on active-active model (service is running on several machines at same time)
► Examples: Clustered Samba, Oracle RAC
► Advantages: Better performance, Everything included Disadvantages: Very difficult to rewrite existing application
Marek Grác xgrac@fi.muni.cz        ATOL: Load Balancing
gp - = = ^)c^o
Framework based solutions
► Application does not know about load-balancing
► Active-active model but YOU HAVE TO take care of data (common storage, persistence of connections)
► ipvsadm
Kernel + user-space part (ipvsadm) Protocol independent
► pulse + piranha
Checking of service availability Improve configuration management piranha (Web User Interface)
Marek Grác xgrac@fi.muni.cz        ATOL: Load Balancing
gp - = = ^)c^o
Protocol specific solutions
Mostly dedicated for HTTP e.g. nginx
Reverse proxy
► Support HTTP, HTTPS, SMTP, POP3, IMAP (nothing else) Used by Sourceforge.net, AOL, WordPress.com
►
Marek Grác xgrac@fi.muni.cz        ATOL: Load Balancing
gp - = = ^)c^o
ipvsadm short FAQ
► kvm virtualization - packet is lost on router between virbrO and ethO is caused by problem with incorrect checksum. On each 'real' server you have to run ethtool -K ethO tx off
► QEMU and XEN virtualization - packet is lost on router between virbrO and ethO - problem is not solved yet
► how to setup arptables? Look at http://sources.redhat.com/cluster/wiki/PiranhaSetupSimple
Marek Grác xgrac@fi.muni.cz        ATOL: Load Balancing
gp - = = ^)c^o
Goals
► Create a load-balancing solution based on ipvsadm on router (IPC) and two load-balanced servers (2PC)
► Create an HTTP service that will be load-balanced (use different text on each server to find out that it works correctly)
Marek Grác xgrac@fi.muni.cz        ATOL: Load Balancing
gp - = = ^)c^o