Traffic Server enables you to control where event log files are located, if and how they will be rotated, and how much space they can consume. The first of these topics is covered in this section, while the latter two will be discussed separately in Log Rotation and Retention.
Two classes of destinations are provided by Traffic Server currently: local and remote. Local logging involves storing log data onto filesystems locally mounted on the same system as the Traffic Server processes themselves and are covered below in Local Logging, while remote logging options involving syslog, are covered below in Remote Logging.
Log Directory Configuration¶
All local logging output is stored within a single base directory.
Individual log file configurations may optionally append
subdirectories to this base path. This location is adjusted with
This configuration may specify either an absolute path on the host (if it
/) or a path relative to the Traffic Server installation directory (any
setting which does not begin with
Traffic Server will need to be restarted, or you will need to run
traffic_ctl config reload for changes to the logging directory to
Local Log Formats¶
Local Traffic Server logs may be emitted in three different formats. The optimal format depends on how administrators intend to use the log data. The first two options, ASCII Log Files and Binary Log Files offer persistent storage of log data, which may be accessed and analyzed by other programs at any time (until the log file’s configured rotation/retention policies, as discussed later in Log Rotation and Retention).
The third option, Named Pipes offers no persistent storage of log data, but rather a live stream of logged events which may be read and interpreted by external processes as they occur.
ASCII Log Files¶
ASCII Traffic Server logs are human-readable, plain-text files with output that is easily
read directly and without the required aid of any additional processing or
conversion tools. By default, log files in this format will have a
Binary Log Files¶
Binary log file output from Traffic Server avoids the conversion overhead of internal
Traffic Server data structures to ASCII strings, but any use of these files by external
programs (or just reading by a human) will first require the use of a converter
application. Binary log files by default will have a
.blog file extension.
In addition to ASCII and binary file modes for custom log formats, Traffic Server
can output log entries in
ASCII_PIPE mode. This mode writes the log entries
to a UNIX named pipe (a buffer in memory). Other processes may read from this
named pipe using standard I/O functions.
The advantage of this mode is that Traffic Server does not need to write the entries to disk, which frees disk space and bandwidth for other tasks. When the buffer is full, Traffic Server drops log entries and issues an error message indicating how many entries were dropped. Because Traffic Server only writes complete log entries to the pipe, only full records are dropped.
Output to named pipes is always, as the mode’s name implies, in ASCII format. There is no option for logging binary format log data to a named pipe.
For ASCII pipes there exists an option to set the
the YAML config.
Deciding Between ASCII or Binary Output¶
Traffic Server offers both ASCII and binary output for log files because each offer advantages under different circumstances. The primary concerns and trade offs that should be considered are covered below. Many of the trade offs between formats will depend heavily on the specific formats you choose for your logs. To make an accurate determination on whether ASCII or binary logging is better for your systems, it is recommended that (with good system and performance monitoring, of course) that you test each format separately under real world traffic.
The only blanket statement that can really be offered in good conscience is that ASCII logging generally offers a lower path of resistance as no additional conversion tools will be necessary.
ASCII logs tend to consume more disk space than their binary counterparts.
Many numeric fields (e.g. content lengths, HTTP status codes, request and
response times, and so on) as well as string representation of IPv4 and IPv6
addresses will consume more bytes than their binary formats. There are
exceptions (a field containing just the value
0 will use a single byte in
an ASCII log, but four bytes in a binary log), so a guarantee cannot be made,
but the general tendency for typical log line formats is to consume slightly
more space in ASCII.
Emitting ASCII format logs does incur some additional processing as the internal Traffic Server data structures for relevant transaction details need to be converted into ASCII strings. While this is usually negligible overhead for most installations, you may wish to compare the performance overhead between emitting ASCII or binary log data if you are very concerned with Traffic Server runtime performance. By using the binary log format, you may gain a very slight amount of proxy performance, at the cost of having to invoke an intermediary converter application every time you wish to view or process the log data.
As mentioned above, any use of the log data by other programs will require the addition of a converter application should you opt for the binary format. If you are frequently ingesting the log data elsewhere, you may not wish to have the time and processing cost of this additional step every time.
If the external program is ingesting the logs continuously, you may wish to use a named pipe output from Traffic Server instead, which is always in ASCII format, but doesn’t have the potentially increased storage needs as there is no persistent storage of the log data involved (at least not by Traffic Server - the application ingesting the data is probably storing its own results somewhere). It also avoids unnecessary disk I/O operations if you only care about the final, analyzed version of the log data and have no permanent use for the intermediate (and raw) output from Traffic Server.
Alternatively, if you wish to hyper-optimize your Traffic Server runtime performance and are only ingesting the log data with an external application on a batched schedule, you might consider logging from Traffic Server using the binary format, then establishing an externally scheduled one-time conversion of the log data to a more easily ingested ASCII format into separate file(s). Coordination of this conversion with the Traffic Server log rotations would be your responsibility.
Traffic Server provides for remote log-shipping functionality, which may be used in addition to or instead of local log storage. This section covers the current options available.
At this time, Traffic Server supports sending log data to syslog only for the system and emergency logs. Sending custom event or transaction error logs to syslog is not directly supported. You may use external log aggregation tools, such as Logstash, to accomplish this by having them handle the ingestion of Traffic Server local log files and forwarding to whatever receivers you wish.