Stop Waiting for Jenkins: Optimizing CI Pipelines on Bare-Metal KVM

There is an old developer joke: "My code is compiling" is the only valid excuse for slacking off. But in 2013, with the rise of Agile and Continuous Integration (CI), that excuse is becoming a liability. If your development team waits 45 minutes for a build loop to complete, you aren't just losing time; you are losing context. By the time the red light flashes in Jenkins, the developer has already context-switched to a different task.

I have seen agile transitions stall completely not because of culture, but because the infrastructure couldn't keep up with the commit frequency. The culprit? usually a cheap, oversold VPS struggling to handle the I/O blender of a modern build pipeline.

In this analysis, we are cutting through the marketing fluff to look at the raw systems engineering required to make Jenkins (or Hudson, if you are still migrating) fly. We will look at file systems, virtualization types, and the specific my.cnf flags that stop your database tests from choking.

1. The I/O Bottleneck: Why Spindles Die

CI workloads are uniquely abusive. Unlike a web server that reads frequently and writes occasionally, a build server does everything at once: checkout (write), compile (read/write), package (write), and run tests (intense random I/O). If you are running this on a standard VPS backed by spinning SAS 15k drives—or worse, SATA—you are in a queue. You are waiting for the physical head of a hard drive to move, while sharing that seek time with 50 other tenants on the host node.

The Solution: Pure SSD.

We ran a benchmark comparing a Magento unit test suite on a standard 7200RPM RAID-10 array versus the Enterprise SSD arrays we use at CoolVDS. The difference wasn't a percentage; it was an order of magnitude.

If your hosting provider charges you extra for "high performance" storage that should be standard, move. SSDs are no longer a luxury in 2013; for CI/CD, they are a requirement.

2. Virtualization: OpenVZ vs. KVM

Many budget VPS providers in Europe love OpenVZ. It allows them to oversell RAM and CPU because it relies on a shared kernel. For a static website, that's fine. For a CI server compiling Java or C++, it's a disaster.

In a heavy build process, you need guaranteed CPU cycles and, more importantly, strict memory isolation. OpenVZ's "burstable" RAM is a trap. When the host node gets busy, your Java Heap allocation might suddenly fail because the memory wasn't actually there.

We strictly utilize KVM (Kernel-based Virtual Machine) at CoolVDS. KVM provides full hardware virtualization. When we allocate 4GB of RAM to your Jenkins instance, that RAM is reserved for you. The kernel is yours. You can load custom modules, tune TCP stacks, and most importantly, you don't suffer from the "noisy neighbor" effect where another user's runaway PHP script steals your compiler's CPU time.

3. Tuning MySQL for Disposable Data

Your integration tests likely spin up a database, insert fixtures, run logic, and tear it down. By default, MySQL is configured for ACID compliance—it wants to ensure data survives a power outage. But for CI tests? We don't care if the data survives a crash. If the server crashes, the build fails anyway. We care about speed.

You can slash your test execution time by telling MySQL to stop being so paranoid. Edit your /etc/my.cnf (or /etc/mysql/my.cnf on Debian/Ubuntu) and apply these settings specifically for your CI environment:

[mysqld]
# 0 = Write to log buffer and flush to disk once per second.
# This is risky for production, but perfect for CI.
innodb_flush_log_at_trx_commit = 0

# Disable the doublewrite buffer to reduce I/O overhead.
innodb_doublewrite = 0

# Keep the table metadata in memory to avoid disk lookups.
table_open_cache = 4000
table_definition_cache = 4000

# Ensure you utilize your RAM (Adjust based on VPS size)
innodb_buffer_pool_size = 2G

Warning: Do not use innodb_flush_log_at_trx_commit = 0 on your production database unless you enjoy data corruption during power failures.

4. The RAM Disk Trick (tmpfs)

Even with SSDs, memory is faster. If your build process generates a lot of temporary files or compilation artifacts that are discarded immediately after, map your workspace to RAM.

You can mount a tmpfs volume directly into your Jenkins workspace. This offloads the heavy write operations from the disk entirely.

# Create a 1GB RAM disk for build artifacts
mount -t tmpfs -o size=1G tmpfs /var/lib/jenkins/workspace/project-build/target

This is particularly effective for the target or build directories in Maven or Ant projects. Just remember that KVM enforces memory limits strictly—if you exceed your allocated RAM, the OOM (Out of Memory) killer will step in. Monitor your usage with htop.

5. Data Sovereignty and Latency

If your dev team is in Oslo or Bergen, why is your CI server in Virginia? Latency kills git operations. A git clone over the Atlantic involves hundreds of TCP round-trips. By hosting locally in Norway, you reduce that latency from ~120ms to <10ms.

Furthermore, we must address the legal landscape. With the Norwegian Data Protection Authority (Datatilsynet) enforcing the Personal Data Act (Personopplysningsloven), and the EU discussions around tightening data privacy (the proposed reform that will replace Directive 95/46/EC), knowing exactly where your data sits is critical. If your CI builds contain production database dumps for testing—a practice I advise against, but know happens—you are processing personal data.

Pro Tip: CoolVDS infrastructure is physically located in secure data centers in Oslo, directly peered at NIX (Norwegian Internet Exchange). Your data stays under Norwegian jurisdiction, and your packets take the shortest path to your office.

Conclusion

Optimizing a CI pipeline isn't just about writing better code; it's about respecting the physics of the underlying hardware. You need high IOPS, dedicated kernel resources, and low network latency.

Don't let a $20 savings on a cheap VPS cost you thousands in developer productivity. If you are ready to stop waiting for builds and start shipping, it is time to upgrade the engine.

Deploy a KVM SSD instance on CoolVDS today. Benchmarks don't lie.