While the default configuration values for ATS will get you up and running,
at the moment they they're somewhat designed for regression testing and not real-world applications.

This page documents what I've discovered myself through a fair amount of experimentation
and experimentation and real-world experience.

The following lists the steps involved in taking a generic configuration,
and  and modifying it for my own needs. Yours may vary, however, and I'll do my best
to indicate which settings should be sized based on your install.

All three Wiki pages use configuration examples from my running home Traffic Server setup.

Current Home Machine

.

Please keep in mind the following only applies to creating a forward-only web proxy caching setup.

The following lists steps involved in taking a generic Traffic Server install and customizing it for my own needs.

NOTE:  Please use the following with Apache Traffic Server v5.0.0 and higher.

 Server Virtual Machine

• Server Host: Vultr (www.vultr.com)Make/Model: Apple iMac Mid 2011
• CPU: 3.4 6 Ghz Intel Core i7 CPU (quad-single core w/Hyperthreading)
• Memory: 8GB1GB
• Disk: 1TB20GB SSD
• OS: Mac OS X v10.8.5CentOS Linux 7.0
• Cache Size: 3GB

...

• : 1GB
• Browser: Google Chrome v43

Testing Regimen

The following settings have been tested against the following:

• IPv4 websites
• IPv6 websites
• Explicitly difficult web pages (i.e. Bing Image Search)
• Explicitly SSL web sites (i.e. Facebook)
• Internet Radio (various typesHTTP streaming, as well as iTunes Radio & Pandora)

The following settings are all located in /usr/local/etc/trafficserver/records.config. When adding lines, simply organize them in alphabetic sequence.

Step 1 – Disable Reverse Proxy

...

Since Traffic Server v5.0.0 has reorganized this file, I'll go through the relevant sections here.  When adding configurations, simply add the settings below the existing ones.

Thread Configuration

As I'm using ATS as purely a forward-only web proxy cacheTraffic Server on a personal basis, I decided to turn these off.
I believe the default settings enable ATS as both a forward and reverse cache.

...

explicitly configure it to not consume as many CPU cores as it might do otherwise.

If your situation is different, simply change proxy.config.

...

exec_

...

thread.limit to set how many CPU cores you'd like to use.

Step 2 – Configure

You may or may not wish to enable these configuration options.
They essentially make ATS more aggressive in caching than its default configuration would allow.

HTTP Background Fill Completion

There's an algorithm here that I don't fully understand, but this setting should guarantee that objects
loaded in the background are cached regardless of their size.

From Leif H: This recommendation is wrong, it should be set to 0.0 for it to always kick in. It allows the server to continue fetching / caching a large object even if the client disconnects. This setting (with a value of 0.0) is a prerequisite for getting read-while-writer to kick in.

CONFIG proxy.config.http.background_fill_completed_threshold FLOAT 0.000000

Fuzzy Object Expiration Logic

From Leif H: As described here, is not what it does, at all. Fuzzy logic is there to allow (random chance) a client to go to origin before the object is stale in cache. The idea is that you would (for some reasonably active objects) prefetch the object such that you always have it fresh in cache.

An interesting notion, but not one I desire. The following setting disables this feature.

CONFIG proxy.config.http.cache.fuzz.min_time INT 0

Step 3 – Optimize

CPU Cores (also multiple CPUs)

The default config for ATS supports up to 2 CPU cores. I have 4, but discovered over time that using all of them
causes problems with iTunes, and World of Warcraft. In the hopes of avoiding problems like that, I decided to
configure my ATS to use just one core where possible.

exec_thread.autoconfig INT 0
CONFIG proxy.config.exec_thread.limit INT 1

HTTP

...

Connection Timeouts

The default config for ATS specifies that the proxy itself use data "chunks" of 4KB each. Being that I'm using Traffic Server on a
high-speed Internet link at home, I decided to increase this. I originally went with 128KB, only to find my
Internet Radio seemed to be having problems. 16KB should remedy that.

CONFIG proxy.config.http.chunking.size INT 16K

HTTP Connection Sharing

The default config for ATS specifies that outbound connections be shared within connection pools
on a per-thread basis. Fair enough. For some reason, though, this caused me no end of performance
problems. Thus, the following specifies one "global" connection pool which is much faster.

CONFIG proxy.config.http.share_server_sessions INT 1

Inbound And Outbound HTTP Connections

The default config for ATS sets these artificially low. I found that remote webservers themselves actually
slow down if more than 16 simultaneous connections are attempted. Also, most popular browsers support
up to 256 simultaneous connections from browser to proxy server so our ATS config should reflect that.

CONFIG proxy.config.http.origin_server_pipeline INT 16
CONFIG proxy.config.http.user_agent_pipeline INT 256

HTTP Connection Timeouts

I decided to use Mozilla Firefox's values here, along with one of my own.
It turns out proxy.config.http.transaction_active_timeout_in was essentially shutting down my
streaming Internet Radio connections. I increased that setting from 15 minutes to 12 hours.

speedy datacenter-grade connection.  As such, I've configured it to be pretty impatient in terms of timeouts.

CONFIG proxy.config.http.keep_alive_no_activity_timeout_in INT 115900
CONFIG proxy.config.http.keep_alive_no_activity_timeout_out INT 115900
CONFIG proxy.config.http.transaction_no_activity_timeout_in INT 905
CONFIG proxy.config.http.transaction_no_activity_timeout_out INT 905
CONFIG proxy.config.http.transaction_active_timeout_in INT 4320014400
CONFIG proxy.config.http.transaction_active_timeout_out INT 4320014400
CONFIG proxy.config.http.accept_no_activity_timeout INT 30

HTTP Cache Options

The following settings are pretty important. I'll go through them one at a time.

This one defines a global variable whose function is to indicate whether specific HTTP headers
are necessary to properly cache an object. As it turns out, much of this functionality is
included in HTTP 1.1 and thus additional headers aren't really necessary.

5
CONFIG proxy.config.net.default_inactivity_timeout INT 5

Network Settings

The following settings control various network-related settings within ATS.

The first setting controls how often Traffic Server will internally poll to process network events.  Even though I'm now on a machine that can handle 2-3% CPU load, I decided to reduce this.  I haven't noticed any significant performance difference as a result of this.

The second and third/fourth settings relate more closely to OS-tuning that's documented in the next wiki page.

The second setting removes the TCP_NODELAY option from origin server connections.  Once one has told Linux to optimize for latency, this appears to be no longer necessary.

The third/fourth settings specify the socket buffer sizes for origin server connections.  I've found setting this to roughly my "average object size" as reported by "traffic_top" appears to be optimal.

CONFIG proxy.config.net.poll_timeout INT 50

CONFIG proxy.config.http.cache.required_headersnet.sock_option_flag_out INT 0

The next specifies how "stale" an object should be before it gets fetched again from the Internet.
The default config for ATS specifies that after 1 week(604800 seconds), any object that is "stale"
should be flushed from the cache. I'd prefer that it stick around for about 3 months.

Cache Control

The following configurations tell Traffic Server to be more aggressive than it would otherwise, with regard to caching overall as well as some speed-ups.

Also, I found that from a correctness point of view, my cache behaves better when not caching "dynamic" URLs.

CONFIG proxy.config.http.cache.max_stale_agecache_urls_that_look_dynamic INT 7776000

This one specifies whether or not to use HTTP "range" requests. While having this option enabled
will save bandwidth, it also slows page loading.

0
CONFIG proxy.config.http.chunking.size INT 64K
CONFIG proxy.config.http.cache.range.lookupims_on_client_no_cache INT 0
CONFIG proxy.config.http.cache.ignore_server_no_cache INT 1

Heuristic Cache Expiration

The default config for ATS Traffic Server specifies that after 1 day(86,400 seconds), any object without a specific expiration
should be flushed from the cache. expiration cannot be cached.

I'd prefer that it they stick around for about 3 monthsbetween 1-4 weeks. This setting is contentious
in that what it should be is debatable.

The goal here is to enforce a window of between 1 and 4 weeks to keep objects in the cache, using Traffic Server's built-in heuristics.

CONFIG proxy.config.http.cache.heuristic_min_lifetime INT 604800
CONFIG proxy.config.http.cache.heuristic_max_lifetime INT 7776000
2592000

Network Configuration

The default config for Traffic Server allows for up to 30,000 simultaneous connections.

I decided for my purposes that's pretty excessiveThere's an algorithm here that I don't fully understand, but this setting should guarantee that the relevant
information regarding an object's "last modified" date is fully support by the cache.

CONFIG proxy.config.httpnet.cache.heuristic_lm_factor FLOAT 1.000000

HTTP RAM Cache

While the default ATS options for this may be optimal under heavy load,
I found using the simpler LRU algorithm much faster and more useful.

The following specifies 1GB of RAM cache, with objects of unlimited size,
to be managed using LRU. During normal use, RAM utilization will rise and rise
until all 1GB is used, then the LRU algorithm should kick in. Also,
figure on at least 100MB of general RAM overhead for ATS in addition to this.

connections_throttle INT 1K

RAM And Disk Cache Configuration

The default config for Traffic Server specifies a few things here that can be tuned.

First, I decided to explicitly set my RAM cache settings.  If your situation is different, simply change proxy.config.ram_cache.size to set how much RAM you'd like to use.

Second, I observed my cache running via the "traffic_top" utility and have set the average object size accordingly.

NOTE:  One should always halve the setting for that configuration, as it allows "headroom" within Traffic Server such that one will never run out of slots in which to store objects.

CONFIG proxy.config.cache.ram_cache.size INT 1G8M
CONFIG proxy.config.cache.ram_cache_cutoff INT 01M
CONFIG proxy.config.cache.ram_cache.algorithm INT 1
CONFIG proxy.config.cache.ram_cache.use_seen_filter INT 0

NOTE: This setting should be sized relative to the amount of memory you want to use.
Also, it requires restarting ATS to properly take effect.

Cache Minimum Average Object Size

This setting is pretty important. It defines a global variable whose function is to both structure the cache
for future objects, as well as optimize other areas. For my purposes, I decided an "average Internet object"
is roughly 32KB in size, and so we can do the following math:

Average Internet Object Size: 32KB
Disk Cache Size: 3GB
Disk Cache Size In Bytes: 3221225472 (3 * 1024 * 1024 * 1024)
Average Internet Object Size In Bytes: 32768 (32 * 1024)
Disk Cache Object Capacity: 98304 (3221225472 / 32768)

CONFIG proxy.config.cache.min_average_object_size INT 96K

NOTE: This setting should be sized relative to the size of your disk cache.
Also, it requires clearing the disk cache and restarting ATS to properly take effect.

Cache Threads Per Disk Spindle

My setting here is somewhat of a rough guess. I've had issues in the past with Squid as a web cache
and increasing the threads dedicated to disk access definitely helped. However, with ATS I've actually
noticed a speed boost by decreasing this setting. My current theory is that this setting should allow
for one thread per CPU core.

24K
CONFIG proxy.config.cache.threadstarget_perfragment_disksize INT 1

Cache Disk Write Lock Delay

The default setting for ATS is unfortunately quite low. For some reason this caused a repeatable,
large delay when loading Bing Image Search results. The following setting removes most of the delays
and seems to speed up the cache overall a bit.

4M
CONFIG proxy.config.cache.mutex_retry_delay INT 50

Maximum Concurrent DNS Queries

The default settings for ATS regarding DNS are set pretty high. I decided for my purposes to lower them,
Your Milage May Vary on these.

CONFIG proxy.config.dnscache.maxenable_dnsread_inwhile_flightwriter INT 512

DNS Internet Protocol Preference

2

Logging Configuration

The defaults for Traffic Server specify a squid-compatible logfile that's binary in nature.  I prefer to have the file readable so I'm overriding thisI've no idea if this setting really helps or not, but I like to specify my preference for IPv6 over IPv4
as much as possible.

CONFIG proxy.config.hostdb.ip_resolve STRING ipv6;ipv4

DNS Host Cache Database Size

The default settings for ATS regarding DNS are set pretty high. I think the following represents a pretty
good balance between caching too much and caching too little in terms of DNS.

CONFIG proxy.config.hostdb.size INT 8K
CONFIG proxy.config.hostdb.storage_size INT 4M

DNS Host Cache Database Timeout

The default config for ATS specifies that after 1 day(1,440 minutes), all DNS records should be flushed
from the cache. I'd prefer that they stick around for about 3 months.

CONFIG proxy.config.hostdb.timeout INT 129600

HTTP Socket I/O Buffers

The default config for ATS leaves these disabled. I believe these to be somewhat useful
for HTTP streaming applications such as Internet Radio and YouTube. However,
setting these too large tends to slow down the cache overall.

log.squid_log_is_ascii INT 1

HostDB Configuration

The defaults for Traffic Server configure the disk-based DNS cache to be rather large.  First, I found I got a decent speed improvement by sizing this down.

Second, I specifically prefer IPv6 over IPv4.  This simply tells the cache to prefer the newer IPv6 when possible.

Third, I also allow the cache to use stale DNS records for up to 60 seconds while they're being updated.  This also contributes to cache speed.

If your situation is different, simply get to know the following settings.  It takes a bit of practice to get used to, but they're all tunable.

##############################################################################
# HostDB
##############################################################################

CONFIG proxy.config.nethostdb.sock_send_buffer_size_in INT 0ip_resolve STRING ipv6;ipv4
CONFIG proxy.config.net.sock_recv_buffer_size_inhostdb.size INT 048K
CONFIG proxy.config.nethostdb.sock_sendstorage_buffer_size_out INT 012M
CONFIG proxy.config.nethostdb.sockserve_recv_buffer_size_out INT 128K

Step 3 – Secure

Maximum Inbound Concurrent Connections

The default config for ATS specifies that this server can handle up to 30,000 connections.
For my purposes, that's a bit excessive. I figure with 1,024 connections there's plenty
of "elbow room".

stale_for INT 60
CONFIG proxy.config.cache.nethostdb.connectionssync_throttlefrequency INT 1K
900

Restart Traffic Server

Once you've updated the relevant records.config settings, simply refresh your disk cache if necessary and then restart Traffic Server.

After that's been done, enjoy your newly-tuned proxy server.

sudo /usr/local/bin/trafficserver stop
sudo /usr/local/bin/trafficserver start

Previous Page:  WebProxyCacheSetup

Next Page: WebProxyCacheOSThat's it. Go ahead and refresh your cache(if necessary), restart ATS, and enjoy your tuned proxy server.