Boris Stoyanov took a look at a load testing exercise conducted in the lab. Discovered how CloudStack performs with 25,000 hosts as we explore response times, performance challenges, and the code improvements needed to scale effectively -- The CloudStack European User Group 2025 took place on May 8th in Vienna, Austria. The event once again brought together open-source cloud professionals, contributors, developers, and users for a day of deep technical insights, knowledge sharing, and community connection.

1. Pushing the Limits:
Cloudstack at 25k hosts
Boris Stoyanov, Shapeblue

2. Objective
• Identify CloudStack’s performance
boundaries under stress
• Pinpoint bottlenecks and
underperforming components
• Lay the groundwork for a repeatable
performance benchmark in future
releases

3. Scope and specifics
• Listing operations
• No active workloads
• Simulated resources
• Virtual Environment

4. Test Environment Setup
• Virtual Environment – dedicated pool
• Simulated hosts, but not cloudstack-
simulator
• Single Management Server
• 25k Hosts
• 25k Instances
• 50k Volumes
• 25k Neworks
• 25k Domains and Accounts

5. Management server
• Oracle Linux 8
• mysql 8.0.36
• ACS 4.20 vanilla
• 2xCPUs 1.5GHz each
• 5GB RAM

6. Tools
• Hosts
• KVM based
• Maintaining connection with
management as regular
cloudstack-agent
• csbench – developed for
Cloudstack
• Provisioning resources
• Benchmark testing

7. Load test
• csbench –benchmark
• Lists(accounts, domains, hosts,
networks, virtualMachines and
volumes)
• 100x
• Observations:
• Response time
• Avarages
• Ratio between 5 and 95 percentile

8. Results
listAccounts
listDomains
listHosts
listNetworks
listVirtualMachines
listVolumes
0 20 40 60 80 100 120
22.94
2.4
5.28
24.11
9.75
4.81
98.48
7.5
12.9
96.92
17.28
14.4
49.63
4.6
7.6
43.57
11.79
9.24
Response time in seconds
Avg Worst Best

9. 95th to 5th ratio
listAccounts
listDomains
listHosts
listNetworks
listVirtualMachines
listVolumes
0 20 40 60 80 100 120
3.68
1.6
1.3
2.9
2.8
1.8
22.94
2.4
5.28
24.11
9.75
4.81
98.48
7.5
12.9
96.92
17.28
14.4
Ratio between best and worst
Worst Best Ratio

10. Takeaways
• Expecting cracks, but we found headspace
• Some APIs perform inconsistently
• Unclear how it behaves in an active env

11. Next Steps
• Emulate workload
• Emulate continuous workload on
the environment under test
• Benchmark more List APIs
• Benchmark workloads – CRUD
APIs
• Make Benchmarking part of
regular release testing

12. Credits
• csbench -
https://github.com/apache/cloudst
ack-csbench
• Contributors: Rohit Yadav,
Vishesh Jindal, Harikrishna
Patnala
• KVM based simulator – Abhishek
Kumar
• Testing – Vladimir Petrov

13. Q&A