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infrequent. For example, if a change happens a few times per hour, being polled every 5
minutes may be sufficient resolution. Pull is also better if it would be useful to have a vari-
able measurement rate, such as a system that polls at a higher frequency when diagnosing
a problem. This approach is analogous to increasing the magnification on a microscope.
Push is better when direct observation is required, such as when we need to know when
somethinghappensratherthanhowmanytimesithashappened.Intheeventofafailure,it
is easier for a push system to store measurements and transmit the backlog when possible.
If it is useful to observe each discrete or specific action, then push is more appropriate.
17.2.2 Protocol Selection
Many different protocols are used in monitoring. The Simple Network Management Pro-
tocol (SNMP) is horrible and should be avoided. Sadly, if you deal with network equip-
ment, it is likely your only choice. If you manage services and machines, there are many
alternatives.
Most of the alternatives are migrating to using JSON transmitted over HTTP. JSON is a
text-based standard for human-readable data interchange. HTTP PUT is used for push and
HTTP GET is used for pull. Because the same JSON data structure is sent in either case, it
simplifies the processing of the data.
SNMP: Simply Not a Management Protocol
We dislike SNMP. Most implementations transmit passwords in clear text and are
inefficientbecausetheytransmitonemeasurementpertransaction.Version3ofthe
protocolcanbesecureandfastbutfewvendorsimplementit.Theprotocoliscom-
plex enough that implementations are a constant source of security-related bugs.
Theadjective“simple”wasintendedtodescribetheprotocol,whichmakesuscon-
cerned what the complex protocol, if it had been invented, would look like. Be-
causeitscalessobadly,wewonderwhether“simple”actuallydescribesthekindof
network it is good for monitoring. The use of the word “management” in its name
has hurt the industry by creating the misperception that managing a network is a
matter of collecting measurements.
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