Debug Tags

Use the API void TSDebug (const char *tag, const char *format_str, ...) to add traces in your plugin. In this API:

  • tag is the Traffic Server parameter that enables Traffic Server to print out “format_str“
  • ... are variables for “format_str“ in the standard printf style.

Run Traffic Server with the -Ttag option. For example, if the tag is my-plugin, then the debug output goes to traffic.out.See below:

traffic_server -T"my-plugin"

Set the following variables in records.config (in the Traffic Server config directory):

CONFIG proxy.config.diags.debug.enabled INT 1
CONFIG proxy.config.diags.debug.tags STRING debug-tag-name

In this case, debug output goes to traffic.out.

Example:

TSDebug ("my-plugin", "Starting my-plugin at %d", the_time);

The statement "Starting my-plugin at <time>" appears whenever you run Traffic Server with the my-plugin tag:

traffic_server -T"my-plugin"

Other Useful Internal Debug Tags

Embedded in the base Traffic Server code are many debug tags for internal debugging purposes. These can also be used to follow Traffic Server behavior for testing and analysis.

The debug tag setting (-T and proxy.config.diags.debug.tags) is a anchored regular expression against which the tag for a specific debug message is matched. This means the value “http” matches debug emssages with the tag “http” but also “http_seq” and “http_trans”. If you want multiple tags then use a pipe symbol to separate the tags. For example “http_tproxy|dns|hostdb” will match any of the message tags “http_tproxy”, “dns”, “hostdb”, or “dns_srv” (but not “http_trans” nor “splitdns”).

Some of the useful HTTP debug tags are:

  • http_hdrs - traces all incoming and outgoing HTTP headers.
  • http_trans - traces actions in an HTTP transaction.
  • http_seq - traces the sequence of the HTTP state machine.
  • http_tproxy - transparency related HTTP events
  • dns - DNS operations
  • hostdb - Host name lookup
  • iocore_net - Socket and low level IO (very voluminous)
  • socket - socket operations
  • ssl - SSL related events
  • cache - Cache operations (many subtags, examine the output to narrow the tag set)
  • cache_update - Cache updates including writes
  • cache_read - Cache read events.
  • dir_probe - Cache searches.
  • sdk - gives some warning concerning API usage.