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Complete Web Monitoring

Cover of Complete Web Monitoring by Alistair Croll... Published by O'Reilly Media, Inc.
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Wrinkles: Why It’s Not Always That Easy

What we’ve just outlined is a relatively straightforward process. If everything goes as planned, the page will load properly. Unfortunately, things often go awry. Much of the work of EUEM is in smoothing out the many wrinkles that can happen along the way.

DNS Latency

DNS can take time to resolve, or fail to resolve entirely. If users can’t get your IP address, they can’t visit you. One of the primary tasks of a web operations team is to manage the propagation of IP addresses through DNS—not just making sure they’re fast, but also that they’re correct and that they can be changed relatively smoothly.

On some systems, you can use the dig command line utility to measure DNS latency (the dig utility is included in the Windows distribution of BIND, available at

macbook:~ alistair$ dig

; <<>> DiG 9.4.2-P2 <<>>
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 23382
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0

;     IN    A

;; ANSWER SECTION: 1800 IN    CNAME     1800 IN    A

;; Query time: 98 msec
;; WHEN: Sat Feb  7 16:25:00 2009
;; MSG SIZE  rcvd: 65

In this example, a DNS lookup for returned a single IP address, and took 98 milliseconds.

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