1. HAProxy - Rate Limiting

    Say you just finished implementing a spam detection mechanism into your popular web service and started responding with HTTP 403s to spam queries.

    This helped to eliminate the load on your database servers, but the sheer amount of abuse queries keeps your web servers busy.

    You decided to employ HAProxy ...

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  2. Three-Generations Release Cycle

    Here is my proposal for a Linux distro release cycle

    • major releases every 2 years
    • point releases (accumulating updates) every year
    • releases happenning on the beginning of the year, ideally on the 1st of January
    • versions based on calendar years - version 10 released in January 2010, version 12 in January ...
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  3. PXE Boot Server on CentOS 6

    To set up a PXE boot server on CentOS 6 we need to install and configure the following

    • DHCP Server
    • TFTP Server
    • Apache HTTP Server
    • Local mirror of a Linux distribution (optional)
    • UPDATE - 2013-04-21 - Added Fedora 18
    • UPDATE - 2013-05-06 - Added Ubuntu 12.04
    • UPDATE - 2013-08-16 - Added Fedora 19, removed Fedora ...
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  4. KVM - Move Guest to Another Host

    Say you got a new KVM hypervisor (kvm02) and want to move a VM to it from an older host (kvm01). You are OK to shut the VM down while the VM is being transfered (this is not a live migration).

    This is what you do:

    On the Old Host ...

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  5. HAProxy - balance uri whole

    HAProxy supports URL hash based load balancing. This is usefull if you want to create a Squid caching cluster and ensure each object is cached only once, thus increasing the cache hit ratio and the number of objects stored in the cluster. To enable the URL hash based load balancing ...

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  6. HAProxy - Performance Tuning

    • use 2 distinct NICs
    • ensure connection tracking is off !!!
    • add to haproxy.cfg
    option http-server-close
    • add to /etc/sysctl.conf
    net.ipv4.ip_local_port_range = 1024 65000
    • If still not good, try the following (or buy a HW load balancer)
    net.ipv4.tcp_tw_reuse = 1
    net.core.somaxconn = 10000
    net.ipv4.tcp_max_syn_backlog = 10000 ...
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