Request a Bosh DNS Alias

AssumptionPermalink

You have my-http-server deployed with an alias setup from the previous story

Recorded values from previous storiesPermalink

BOSH_DNS_IP=<value>
NON_BOSH_DNS_IP=<value>
HTTP_SERVER_ALIAS=<value>

WhatPermalink

In this story you are going to look at what happens under the hood when you do a DNS request for HTTP_SERVER_ALIAS.

HowPermalink

📝 Do a DNS lookup for your alias

Bosh ssh onto any Cloud Foundry VM

Use dig to do a DNS request for your alias.

dig HTTP_SERVER_ALIAS

Returns:

; <<>> DiG 9.10.3-P4-Ubuntu <<>> meow.meow
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 28967
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;meow.meow.      IN  A

;; ANSWER SECTION:
meow.meow.   0 IN  A 10.0.1.23   # <------------ This should match the IP of one of the my-http-server VMs
meow.meow.    0 IN  A 10.0.1.22   # <------------ This should match the IP of the other my-http-server VM

;; Query time: 2 msec
;; SERVER: 169.254.0.2#53(169.254.0.2)        # <------------ This should match the BOSH_DNS_IP
;; WHEN: Thu Oct 03 20:45:06 UTC 2019
;; MSG SIZE  rcvd: 83

📝 Look at logs

Look at the bosh-dns logs on the machine you did the dig on in the steps above
```
tail -f /var/vcap/sys/log/bosh-dns/bosh_dns*
```
Returns:
```
[RequestLoggerHandler] 2019/10/03 20:49:43
INFO - handlers.DiscoveryHandler Request [1]
[amelia.meow.] 0 160000ns                     # <------------ Note, there is no recursor
```
- ❓ Remember how with neopets.com there was a recursor in the logs? Based on what you know about recursors, why do you think there is no recursor listed in this log line?

📝 Tell dig what DNS server to use

Try digging your alias again, but this time force dig to use the BOSH_DNS_IP as the DNS server
- ❓ Does this succeed? Why or why not?
Try digging your alias again, but this time force dig to use the NON_BOSH_DNS_IP as the DNS server
- ❓ Does this succeed? Why or why not?

Expected ResultsPermalink

The Bosh DNS server knows how to recurse to the non-Bosh DNS server. However, the non-Bosh DNS server does not recurse to the Bosh DNS server. Because of this, the non-Bosh DNS server will not be able to resolve HTTP_SERVER_ALIAS.

Helpful CommandPermalink

Do a DNS lookup

   dig URL [@SERVER_IP]

   # for example
   dig neopets.com
   # OR
   dig neopets.com @169.254.4.4