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FAQs

How do you create a raw disk for the cache if all your disks have mounted file systems?

Link to documentation

How do disk I/O errors affect the cache and what does Traffic Server do when a cache disk fails?

If a disk drive fails five successive I/O operations, then Traffic Server considers the drive inaccessible and removes the entire disk from the cache. Normal cache operations continue for all other Traffic Server disk drives.

If a client disconnects during the time that Traffic Server is downloading a large object, is any of the object saved in the cache?

When a client disconnects during an HTTP operation, Traffic Server continues to download the object from the origin server for up to 10 seconds. If the transfer from the origin server completes successfully within 10 seconds after the client disconnect, then Traffic Server stores the object in cache. If the origin server download does not complete successfully within 10 seconds, then Traffic Server disconnects from the origin server and deletes the object from cache. Traffic Server does not store partial documents in the cache.

Can Traffic Server cache Java applets, JavaScript programs, or other application files like VBScript?

Yes, Traffic Server can store and serve Java applets, JavaScript programs, VBScripts, and other executable objects from its cache according to the freshness and cacheability rules for HTTP objects. Traffic Server does not execute the applets, scripts, or programs, however - these objects run only when the client system (ie, the one that sent the request) loads them.

How do you apply changes to the logs_xml.config file to all nodes in a cluster?

Link to documentation

In Squid- and Netscape-format log files, what do the cache result codes mean?

This is described in detail in the Squid log format documentation

What is recorded by the cqtx field in a custom log file?

  • In forward proxy mode, the cqtx field records the complete client request in the log file (for example, GET http://www.company.com HTTP/1.0 ).
  • In reverse proxy mode, the cqtx field records the hostname or IP address of the origin server because Traffic Server first remaps the request as per map rules in the remap.config file.

Does Traffic Server refresh entries in its host database after a certain period of time if they have not been used?

By default, the Traffic Server host database observes the time-to-live (ttl) values set by name servers. You can reconfigure Traffic Server to ignore the ttl set by name servers and use a specific Traffic Server setting instead. Alternatively, you can configure Traffic Server to compare the ttl value set by the name server with the ttl value set by Traffic Server, and then use either the lower or the higher value.

see proxy.config.hostdb.ttl_mode for more info

Can you improve the look of your custom response pages by using images, animated .gifs, and Java applets?

No, because Traffic Server can only respond to clients with a single text or HTML document. As a workaround, however, you can provide references on your custom response pages to images, animated .gifs, Java applets, or objects other than text which are located on a web server. Add links in the body_factory template files in the same way you would for any image in an HTML document (i.e., with the full URL in the SRC attribute).

Can Traffic Server run in forward proxy and reverse proxy modes at the same time?

Yes. When you enable reverse proxy mode, Traffic Server remaps incoming requests according to the map rules in the remap.config file. All other requests that do not match a map rule are simply served in forward proxy mode.

If you want to run in reverse proxy only mode (wherein Traffic Server does not serve requests that fail to match a map rule), then you must set the configuration variable proxy.config.url_remap.remap_required to 1 in the records.config file.

How do I enable forward proxy mode

Please refer to the Forward Proxy documentation

How do I interpret the Via: header code?

The Via header is an optional HTTP header added by Traffic Server and other HTTP proxies. If a request goes through multiple proxies, each one appends its Via header content to the end of the existing Via header. Via header content is for general information and diagnostic use only and should not be used as a programmatic interface to Traffic Server.

The form of the Via header is

Via: <protocol> <proxyname> (<product/version> [<via-codes>]
  • the scheme and version of the HTTP request
  • the configured name of the proxy server (defaults to the hostname of the machine where it was built)
  • Traffic Server and its version
  • a string of alphabetic codes presenting status information about the proxy handling of the HTTP request

For example:

Via: HTTP/1.0 storm (Traffic-Server/4.0.0   [cMs f ])
      [u lH o  f  pS eN]     cache hit
      [u lM oS fF pS eN]     cache miss
      [uN l oS f  pS eN]     no-cache origin server fetch

The short status code shows the cache-lookup, server-info and cache-fill information as listed in the full status code description below. The long status code list can be achieved by setting proxy.config.http.insert_request_via_str to a higher value.

The character strings in the via-code show [<request results>:<proxy op>] where represents status information about the results of the client request and represent some information about the proxy operations performed during request processing. The full via-code status format is

[u<client-info> c<cache-lookup> s<server-info> f<cache-fill> p<proxy-info> e<error-codes> : t<tunnel-info>c<cache-type><cache-lookup-result> i<icp-conn-info> p<parent-proxy> s<server-conn-info>]

u client-info Request headers received from client. Value is one of:

C
cookie
E
error in request
I
If Modified Since (IMS)
N
no-cache
S
simple request (not conditional)

c cache-lookup Result of Traffic Server cache lookup for URL. Value is one of:

A
in cache, not acceptable (a cache "MISS")
H
in cache, fresh (a cache "HIT")
M
miss (a cache "MISS")
S
in cache, stale (a cache "MISS")
blank
no cache lookup performed

s server-info Response information received from origin server. Value is one of:

E
error in response
N
not-modified
S
served
blank
no server connection needed

f cache-fill Result of document write to cache. Value is one of:

D
cached copy deleted
U
updated old cache copy
W
written into cache (new copy)
blank
no cache write performed

p proxy-info Proxy operation result. Value is one of:

N
not-modified
R
origin server revalidated
S
served

e error-codes Value is one of:

A
authorization failure
C
connection to server failed
D
dns failure
F
request forbidden
H
header syntax unacceptable
N
no error
S
server related error
T
connection timed out

: = Separates proxy request result information from operation detail codes

t tunnel-info Proxy-only service operation. Value is one of:

F
tunneling due to a header field (such as presence of If-Range header)
M
tunneling due to a method (e.g. CONNECT)
O
tunneling because cache is turned off
U
tunneling because of url (url suggests dynamic content)
blank
no tunneling

c cache-type and cache-lookup cache result values (2 characters)

cache-type character value is one of

C
cache
I
icp
blank
cache miss or no cache lookup

cache-lookup-result character value is one of:

C
cache hit, but config forces revalidate
D
cache hit, but method forces revalidated (e.g. ftp, not anonymous)
H
cache hit
I
conditional miss (client sent conditional, fresh in cache, returned 412)
M
cache miss (url not in cache)
N
conditional hit (client sent conditional, doc fresh in cache, returned 304)
S
cache hit, but expired
U
cache hit, but client forces revalidate (e.g. Pragma: no-cache)
blank
no cache lookup

i icp-conn-info ICP status

F
connection open failed
S
connection opened successfully
blank
no icp

p parent-proxy parent proxy connection status

F
connection open failed
S
connection opened successfully
blank
no parent proxy

s server-conn-info origin server connection status

F
connection open failed
S
connection opened successfully
blank
no server connection

Support for HTTP Expect: Header

Traffic Server currently does not handle request Expect: headers according to the HTTP/1.1 spec.

Note that clients such as cURL automatically send Expect: for POST requests with large POST bodies, with a 1 second timeout if a 100 Continue response is not received. To avoid the timeout when using cURL as a client to Traffic Server, you can turn off the Expect: header as follows:

command line:

curl -H"Expect:" http://www.example.com/

C (libcurl):

struct curl_slist *header_list=NULL;
header_list = curl_slist_append(header_list, "Expect:");
curl_easy_setopt(my_curlp, CURLOPT_HTTPHEADER, header_list);

php:

curl_setopt($ch, CURLOPT_HTTPHEADER, array('Expect:'));

Troubleshooting Tips

The throughput statistic is inaccurate

Traffic Server updates the throughput statistic after it has transferred an entire object. For larger files, the byte count increases sharply at the end of a transfer. The complete number of bytes transferred is attributed to the last 10-second interval, although it can take several minutes to transfer the object. This inaccuracy is more noticeable with a light load. A heavier load yields a more accurate statistic.

You are unable to execute Traffic Line commands

Traffic Line commands do not execute under the following conditions:

  • When the traffic_manager process is not running Check to see if the **traffic_manager** process is running by entering the following command: ps aux | grep traffic_manager

If the traffic_manager process is not running, then enter the following command from the Traffic Server bin directory to start it: ./traffic_manager

You should always start and stop Traffic Server with the start_traffic_serverand stop_traffic_server commands to ensure that all the processes start and stop correctly. For more information, refer to Getting Started. When you are not executing the command from $TSHome/bin If the Traffic Server bin directory is not in your path, then prepend the Traffic Line commands with ./ (for example, ./traffic_line -h). When multiple Traffic Server installations are present and you are not executing the Traffic Line command from the active Traffic Server path specified in /etc/traffic_server

You observe inconsistent behavior when one node obtains an object from another node in the cluster

As part of the initial system preparation, you must synchronize the clocks on all nodes in your cluster. Minor time differences do not cause problems, but differences of more than a few minutes can affect Traffic Server operation.

You should run a clock synchronization daemon such as xntpd. To obtain the latest version of xntpd, go to http://www.eecis.udel.edu/~ntp/

Web browsers display an error document with a 'data missing' message

A message similar to the following might display in web browsers:

  Data Missing

This document resulted from a POST operation and has expired from the cache. You can repost the form data to recreate the document by pressing the Reload button.

This is a Web browser issue and not a problem specific to (or caused by) Traffic Server. Because Web browsers maintain a separate local cache in memory and/or disk on the client system, messages about documents that have expired from cache refer to the browser's local cache and _not _ to the Traffic Server cache. There is no Traffic Server message or condition that can cause such messages to appear in a web browser.

Traffic Server does not resolve any websites

The browser indicates that it is contacting the host and then times out with the following message:

    The document contains no data; Try again later, or contact the server's Administrator...

Make sure the system is configured correctly and that Traffic Server can read the name resolution file:

  • Check if the server can resolve DNS lookups by issuing the nslookup command (for example, nslookup www.myhost.com).
  • Check if the /etc/resolv.conf file contains valid IP addresses for your DNS servers.
  • On some systems, if the /etc/resolv.conf file is unreadable or has no name server entry, then the operating system uses localhost as a name server. Traffic Server, however, does not use this convention. If you want to use localhost as a name server, then you must add a name server entry for 127.0.0.1 or 0.0.0.0 in the /etc/resolv.conf file.
  • Check that the Traffic Server user account has permission to read the /etc/resolv.conf file. If it does not, then change the file permissions to rw-r--r-- (644)

'Maximum document size exceeded' message in the system log file

The following message appears in the system log file:

     WARNING: Maximum document size exceeded

A requested object was larger than the maximum size allowed in the Traffic Server cache, so Traffic Server provided proxy service for the oversized object but did not cache it. To set the object size limit for the cache, modify the proxy.config.cache.limits.http.max_doc_size variable in the records.config file. If you do not want to limit the size of objects in the cache, then set the document size to**0**(zero).

'DrainIncomingChannel' message in the system log file

The following messages may appear in the system log file:

 Feb 20 23:53:40 louis traffic_manager[4414]: ERROR ==> [drainIncomingChannel] Unknown message: 'GET http://www.telechamada.pt/ HTTP/1.0'
 Feb 20 23:53:46 louis last message repeated 1 time 
 Feb 20 23:53:58 louis traffic_manager[4414]: ERROR ==> [drainIncomingChannel] Unknown message: 'GET http://www.ip.pt/ HTTP/1.0'

These error messages indicate that a browser is sending HTTP requests to one of the Traffic Server cluster ports - either rsport (default port 8088) or mcport (default port 8089). Traffic Server discards the request; this error does not cause any Traffic Server problems. The misconfigured browser must be reconfigured to use the correct proxy port. Traffic Server clusters work best when configured to use a separate network interface and cluster on a private subnet, so that client machines have no access to the cluster ports.

'No cop file' message in the system log file

The following message appears repeatedly in the system log file:

 traffic_cop[16056]: encountered "config/internal/no_cop" file...exiting

The file config/internal/no_cop acts as an administrative control that instructs the traffic_cop process to exit immediately without starting traffic_manager or performing any health checks. The no_cop file prevents Traffic Server from starting automatically when it has been stopped with the stop_traffic_server command. Without this static control, Traffic Server would restart automatically upon system reboot. The no_cop control keeps Traffic Server off until it is explicitly restarted with the

start_traffic_server

command.

The Traffic Server installation script also creates a no_cop file so that Traffic Server does not start automatically. After you have completed installation/configuration and have rebooted the operating system, use the

  start_traffic_server

command to start Traffic Server.

Warning in the system log file when manually editing vaddrs.config

If you manually edit the vaddrs.config file as a non-root user, then Traffic Server issues a warning message in the system log file similar to the following:

     WARNING: interface is ignored: Operation not permitted

You can safely ignore this message; Traffic Server does apply your configuration edits.

Traffic Server is running but no log files are created

Traffic Server only writes event log files when there is information to record. If Traffic Server is idle, then it's possible/probable that no log files exist. In addition:

Make sure you're looking in the correct directory. By default, Traffic Server creates log files in the logs directory. Check the location of log files by checking the value of the variable proxy.config.log.logfile_dir in the records.config file. Check that the log directory has read/write permissions for the Traffic Server user account. If the log directory does not have the correct permissions, then the traffic_server process is unable to open or create log files. Check that logging is enabled by checking the value of the proxy.config.log.logging_enabled variable in the records.config file. Check that a log format is enabled. In the records.config file, select the standard or custom format by editing variables in the Logging Config section.

Traffic Server shows an error indicating too many network connections

By default, Traffic Server supports 8000 network connections: half of this number is allocated for client connections and the remaining half is for origin server connections. A connection throttle event occurs when client or origin server connections reach 90% of half the configured limit (3600 by default). When a connection throttle event occurs, Traffic Server continues processing all existing connections but will not accept new client connection requests until the connection count falls below the limit.

Connection throttle events can occur under the following conditions:

  • If there is a connection spike (e.g., if thousands of client requests all reach Traffic Server at the same time). Such events are typically transient and require no corrective action.
  • If there is a service overload (e.g., if client requests continuously arrive faster than Traffic Server can service them). Service overloads often indicate network problems between Traffic Server and origin servers. Conversely, it may indicate that Traffic Server needs more memory, CPU, cache disks, or other resources to handle the client load.

If necessary, you can reset the maximum number of connections supported by Traffic Server by editing the value of the _proxy.config.net.connections_throttle _ configuration variable in the records.config file. Do not increase the connection throttle limit unless the system has adequate memory to handle the client connections required. A system with limited RAM might need a throttle limit lower than the default value. Do not set this variable below the minimum value of 100.

Low memory symptoms

Under heavy load, the Linux kernel can run out of RAM. This low memory condition can cause slow performance and a variety of other system problems. In fact, RAM exhaustion can occur even if the system has plenty of free swap space.

Symptoms of extreme memory exhaustion include the following messages in the system log files (/var/log/messages):

 WARNING: errno 105 is ENOBUFS (low on kernel memory), consider a memory upgrade `kernel: eth0: can't fill rx buffer (force 0)!
 kernel: recvmsg bug: copied E01BA916 seq E01BAB22

To avoid memory exhaustion, add more RAM to the system or reduce the load on Traffic Server.

Connection timeouts with the origin server

Certain origin servers take longer than 30 seconds to post HTTP requests, which results in connection timeouts with Traffic Server. To prevent such connection timeouts, you must change the value of the configuration variable proxy.config.http.connect_attempts_timeout in the records.config file to 60 seconds or more.