external/og-aws
1
0
Fork 0
mirror of https://github.com/nickpoida/og-aws.git synced 2025-02-15 03:11:57 +00:00
Code Issues Releases Wiki Activity

Merge pull request #321 from ram-nadella/clb-nginx-gotcha-update

Browse source 
Update note about nginx gotcha in the CLB section
This commit is contained in:
Joshua Levy 2016-11-20 19:17:32 -08:00 committed by GitHub
commit d824ce1e62
1 changed files with 1 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
README.md
View file

@ -927,7 +927,7 @@ Load Balancers
### Load Balancer Gotchas and Limitations
- ❗CLBs and ALBs have **no fixed external IP** that all clients see. For most consumer apps this doesn’t matter, but enterprise customers of yours may want this. IPs will be different for each user, and will vary unpredictably for a single client over time (within the standard [EC2 IP ranges](http://docs.aws.amazon.com/general/latest/gr/aws-ip-ranges.html)). And similarly, never resolve an CLB name to an IP and put it as the value of an A record — it will work for a while, then break!
- ❗Some web clients or reverse proxies cache DNS lookups for a long time, which is problematic for CLBs and ALBs, since they change their IPs. This means after a few minutes, hours, or days, your client will stop working, unless you disable DNS caching. Watch out for [Java’s settings](http://docs.oracle.com/javase/8/docs/api/java/net/InetAddress.html) and be sure to [adjust them properly](http://docs.aws.amazon.com/AWSSdkDocsJava/latest/DeveloperGuide/java-dg-jvm-ttl.html). Another example is nginx as a reverse proxy, which [resolves backends only at start-up](https://www.jethrocarr.com/2013/11/02/nginx-reverse-proxies-and-dns-resolution/).
- ❗Some web clients or reverse proxies cache DNS lookups for a long time, which is problematic for CLBs and ALBs, since they change their IPs. This means after a few minutes, hours, or days, your client will stop working, unless you disable DNS caching. Watch out for [Java’s settings](http://docs.oracle.com/javase/8/docs/api/java/net/InetAddress.html) and be sure to [adjust them properly](http://docs.aws.amazon.com/AWSSdkDocsJava/latest/DeveloperGuide/java-dg-jvm-ttl.html). Another example is nginx as a reverse proxy, which [normally resolves backends only at start-up](https://www.jethrocarr.com/2013/11/02/nginx-reverse-proxies-and-dns-resolution/) (although there is [a way to get around this](https://tenzer.dk/nginx-with-dynamic-upstreams/)).
- ❗It’s not unheard of for IPs to be recycled between customers without a long cool-off period. So as a client, if you cache an IP and are not using SSL (to verify the server), you might get not just errors, but responses from completely different services or companies!
- 🔸As an operator of a service behind an CLB or ALB, the latter phenomenon means you can also see puzzling or erroneous requests by clients of other companies. This is most common with clients using back-end APIs (since web browsers typically cache for a limited period).
- ❗CLBs and ALBs take time to scale up, it does not handle sudden spikes in traffic well. Therefore, if you anticipate a spike, you need to “pre-warm” the load balancer by gradually sending an increasing amount of traffic.