Skip to main content

Jmeter-Terraform - Dealing with AWS ELB IP changes during load testing

We ran into an issue when trying to load test our 'new' production environment - the ELB IP addresses change as it silently auto-scales.  And since you're throwing load at it, of course those IPs will change!

When we started the tests, we had updated the hosts file on the master/slave Jmeter nodes, but of course at some point during the day the IPs changed and we got a pile of timeouts.  After much gnashing of teeth, we found the DNS Cache Manager in Jmeter, and figured there were two solutions:

  1. Use the DNS Cache Manager to point to a custom DNS server (that we set up), and have that DNS server deal with keeping the IPs up to date.
  2. Write a cron job to run on each node that updates the hosts file, then use the DNS Cache Manager to 'clear cache on each iteration'
We elected to do #2 (since our Jmeter infra is built/destroyed a lot, it didn't make sense to have another server in the mix), and here's what we ended up with.

Terraform applies userdata to each EC2 instance, so we simply added a file and a command to that. (don't judge me on Linux security, k? :) )

- encoding: b64
content: base64encodedgoobliehere
owner: root:root
path: /root/updatedns.sh
permissions: 0644

Then in the runcmd section:
- (crontab -l ; echo "* * * * * /bin/sh /root/updatedns.sh") | sort - | uniq - | crontab -

The file contents:
grep -n 'myrealproddomain.com' /etc/hosts && sed -i "s/\(.*\)myrealproddomain.com/$(dig elb-name-and-id.aws-region.elb.amazonaws.com | grep "IN A" | awk '{ print $5 }' | head -n 1) myrealproddomain.com/g" /etc/hosts || echo $(dig elb-name-and-id.aws-region.elb.amazonaws.com | grep "IN A" | awk '{ print $5 }' | head -n 1) myrealproddomain.com >> /etc/hosts

Where 'myrealproddomain.com' is your production domain name (in our case, we only had to deal with one domain to falsify), and 'elb-name-and-id.aws-region.elb.amazonaws.com' is of course the A record that AWS provides you for the ELB.

It's ghetto, but darn it if it doesn't work.  You still have the chance that the IPs will change and you might have to wait up to 60s for that to remediate, but that's better than an entire test run bombing out.

Comments

Popular posts from this blog

DFSR - eventid 4312 - replication just won't work

This warning isn't documented that well on the googles, so here's some google fodder:


You are trying to set up replication for a DFS folder (no existing replication)Source server is 2008R2, 'branch office' server is 2012R2 (I'm moving all our infra to 2012R2)You have no issues getting replication configuredYou see the DFSR folders get created on the other end, but nothing stagesFinally you get EventID 4312:
The DFS Replication service failed to get folder information when walking the file system on a journal wrap or loss recovery due to repeated sharing violations encountered on a folder. The service cannot replicate the folder and files in that folder until the sharing violation is resolved.  Additional Information:  Folder: F:\Users$\user.name\Desktop\Random Folder Name\  Replicated Folder Root: F:\Users$  File ID: {00000000-0000-0000-0000-000000000000}-v0  Replicated Folder Name: Users  Replicated Folder ID: 33F0449D-5E67-4DA1-99AC-681B5BACC7E5  Replication Group…

Fixing duplicate SPNs (service principal name)

This is a pretty handy thing to know:

SPNs are used when a specific service/daemon uses Kerberos to authenticate against AD. They map a specific service, port, and object together with this convention: class/host:port/name

If you use a computer object to auth (such as local service):
MSSQLSVC/tor-sql-01.domain.local:1433

If you use a user object to auth (such as a service account, or admin account):
MSSQLSVC/username:1433

Why do we care about duplicate SPNs? If you have two entries trying to auth using the same Kerberos ticket (I think that's right...), they will conflict, and cause errors and service failures.

To check for duplicate SPNs:
The command "setspn.exe -X

C:\Windows\system32>setspn -X
Processing entry 7
MSSQLSvc/server1.company.local:1433 is registered on these accounts:
CN=SERVER1,OU=servers,OU=resources,DC=company,DC=local
CN=SQL Admin,OU=service accounts,OU=resources,DC=company,DC=local

found 1 groups of duplicate SPNs. (truncated/sanitized)

Note that y…

Logstash to Nagios - alerting based on Windows Event ID

This took way longer than it should have to get going...so here's a config and brain dump...

Why?
You want to have a central place to analyze Windows Event/IIS/local application logs, alert off specific events, alert off specific situations.  You don't have the budget for a boxed solution.  You want pretty graphs.  You don't particularly care about individual server states.  (see rationale below - although you certainly have all the tools here to care, I haven't provided that configuration)

How?
ELK stack, OMD, NXlog agent, and Rsyslog.  The premise here is as follows:

Event generated on server into EventLogNXlog ships to Logstash inputLogstash filter adds fields and tags to specified eventsLogstash output sends to a passive Nagios service via the Nagios NSCA outputThe passive service on Nagios (Check_MK c/o OMD) does its thing w. alerting
OMD
Open Monitoring Distribution, but the real point here is Check_MK (IIRC Icinga uses this...).  It makes Nagios easy to use and main…