Scaling OKD HAProxy Router

Baseline Performance

The OKD router is the ingress point for all external traffic destined for OKD services.

When evaluating a single HAProxy router performance in terms of HTTP requests handled per second, the performance varies depending on many factors. In particular:

  • HTTP keep-alive/close mode,

  • route type

  • TLS session resumption client support

  • number of concurrent connections per target route

  • number of target routes

  • backend server page size

  • underlying infrastructure (network/SDN solution, CPU, and so on)

While performance in your specific environment will vary, our lab tests on a public cloud instance of size 4 vCPU/16GB RAM, a single HAProxy router handling 100 routes terminated by backends serving 1kB static pages is able to handle the following.

In HTTP keep-alive mode scenarios:

Encryption HTTP(s) requests per second

none

22577

edge

11642

passthrough

33335

re-encrypt

11521

In HTTP close (no keep-alive) scenarios:

Encryption HTTP(s) requests per second

none

5771

edge

1780

passthrough

3488

re-encrypt

1248

TLS session resumption was used for encrypted routes. With HTTP keep-alive, a single HAProxy router is capable of saturating 1 Gbit NIC at page sizes as small as 8 kB.

When running on bare metal with modern processors, you can expect roughly twice the performance of the public cloud instance above. This overhead is introduced by the virtualization layer in place on public clouds and holds mostly true for private cloud-based virtualization as well. The following table is a guide on how many applications to use behind the router:

Number of applications Application type

5-10

static file/web server or caching proxy

100-1000

applications generating dynamic content

In general, HAProxy can saturate about 5-1000 applications, depending on the technology in use. The number will typically be lower for applications serving only static content.

Router sharding should be used to serve more routes towards applications and help horizontally scale the routing tier.

Performance Optimizations

Setting the Maximum Number of Connections

One of the most important tunable parameters for HAProxy scalability is the maxconn parameter, which sets the maximum per-process number of concurrent connections to a given number. Adjust this parameter by editing the ROUTER_MAX_CONNECTIONS environment variable in the OKD HAProxy router’s deployment configuration file.

A connection includes the frontend and internal backend. This counts as two connections. Be sure to set ROUTER_MAX_CONNECTIONS to double than the number of connections you intend to create.

CPU and Interrupt Affinity

In OKD, the HAProxy router runs as a single process. The OKD HAProxy router typically performs better on a system with fewer but high frequency cores, rather than on an symmetric multiprocessing (SMP) system with a high number of lower frequency cores.

Pinning the HAProxy process to one CPU core and the network interrupts to another CPU core tends to increase network performance. Having processes and interrupts on the same non-uniform memory access (NUMA) node helps avoid memory accesses by ensuring a shared L3 cache. However, this level of control is generally not possible on a public cloud environment. On bare metal hosts, irqbalance automatically handles peripheral component interconnect (PCI) locality and NUMA affinity for interrupt request lines (IRQs). On a cloud environment, this level of information is generally not provided to the operating system.

CPU pinning is performed either by taskset or by using HAProxy’s cpu-map parameter. This directive takes two arguments: the process ID and the CPU core ID. For example, to pin HAProxy process 1 onto CPU core 0, add the following line to the global section of HAProxy’s configuration file:

    cpu-map 1 0

To modify the HAProxy configuration file, refer to Deploying a Customized HAProxy Router.

Impacts of Buffer Increases

The OKD HAProxy router request buffer configuration limits the size of headers in incoming requests and responses from applications. The HAProxy parameter tune.bufsize can be increased to allow processing of larger headers and to allow applications with very large cookies to work, such as those accepted by load balancers provided by many public cloud providers. However, this affects the total memory use, especially when large numbers of connections are open. With very large numbers of open connections, the memory usage will be nearly proportionate to the increase of this tunable parameter.

Optimizations for HAProxy Reloads

Long-lasting connections, such as WebSocket connections, combined with long client/server HAProxy timeouts and short HAProxy reload intervals, can cause instantiation of many HAProxy processes. These processes must handle old connections, which were started before the HAProxy configuration reload. A large number of these processes is undesirable, as it will exert unnecessary load on the system and can lead to issues, such as out of memory conditions.

Router environment variables affecting this behavior are ROUTER_DEFAULT_TUNNEL_TIMEOUT, ROUTER_DEFAULT_CLIENT_TIMEOUT, ROUTER_DEFAULT_SERVER_TIMEOUT, and RELOAD_INTERVAL in particular.