Masakari in OpenStack: High Availability for Your Cloud

In the world of cloud computing, high availability (HA) is not a luxury—it's a necessity. When you're running critical applications on virtual machines, downtime can mean lost revenue, damaged reputation, or worse. That's where Masakari, OpenStack’s high availability service, steps in. Designed specifically for managing and recovering virtual machines (VMs) in failure scenarios, Masakari helps keep cloud environments resilient, automated, and always-on. 

Let’s explore what Masakari is, how it works, and why it matters in an OpenStack deployment. 

🚀 What Is Masakari? 

Masakari is an OpenStack project that provides automated recovery of virtual machine instances in case of failure. The name "Masakari" (マサカリ) comes from a Japanese word for "battle axe"—a nod to its decisive role in cutting through VM failures quickly and efficiently. 

The service focuses on instance-level HA, meaning it doesn't manage the whole host or infrastructure but instead keeps an eye on the VMs themselves. If a virtual machine goes down unexpectedly—due to a host crash, a process failure, or even a VM-level failure—Masakari will automatically recover the affected instances by restarting or migrating them, depending on the type of failure and the policy in place. 

Masakari is especially useful in environments that need to meet strict SLAs or provide continuous services to users, such as telecom clouds, enterprise apps, or e-commerce platforms. 

🧠 How Does Masakari Work? 

Masakari operates as a set of monitoring and recovery components that continuously scan the OpenStack compute infrastructure. It's built around a modular architecture and integrates seamlessly with Nova (the compute service) and other core OpenStack components. 

There are three primary failure types Masakari handles: 

Host Failure Recovery 

This occurs when an entire compute node (i.e., the physical server running virtual machines) fails. Masakari detects this through monitoring and attempts to recover all the instances that were running on the failed host by restarting them on healthy hosts. 

Process Failure Recovery 

Sometimes, the compute host is fine, but a key service (like the Nova compute service) crashes. Masakari can detect this kind of process-level failure and recover affected VMs accordingly. 

Instance Failure Recovery 

In this scenario, the VM process itself crashes or stops responding, even if the host and services are healthy. Masakari can restart or migrate the instance based on configured policies. 

🧩 Masakari Architecture and Components 

Masakari consists of several moving parts, each playing a crucial role: 

🔹 Masakari API 

The REST API used to interact with Masakari. It receives failure notifications from external monitors (like Monasca or a custom script) and manages recovery workflows. 

🔹 Masakari Engine 

This is the brain of the system. It processes failure notifications and initiates the appropriate recovery actions—whether that’s rebooting a VM, live migrating it, or taking other steps based on defined policies. 

🔹 Masakari Monitors 

While Masakari doesn’t include built-in monitoring tools, it relies on external tools to detect failures and send alerts. Common integrations include: 

• Monasca: OpenStack’s monitoring-as-a-service solution 

• Pacemaker/Corosync: Used for traditional high availability in Linux environments 

• Custom scripts: For tailored health checks and failure detection 

These monitors detect failure conditions and push them to the Masakari API, triggering recovery. 

🔄 Recovery Workflow 

Here’s a simplified look at how Masakari handles a failure: 

1. A monitor (e.g., Monasca) detects that a compute host or VM has failed. 

2. It sends a notification to the Masakari API. 

3. The Masakari engine processes the notification and begins the recovery workflow. 

4. Based on the type of failure and recovery policy, Masakari interacts with Nova to: 

1. Reboot the VM 

2. Evacuate the VM to another host 

3. Migrate the VM to a healthier node 

5. The system logs the recovery actions and status updates for visibility and auditability. 

⚙️ Configuration and Policies 

Masakari allows for flexible recovery policies that define how different types of failures should be handled. These policies can include: 

• Automatic evacuation (moving a VM to a new host after failure) 

• Automatic reboot (restarting the VM on the same or a different host) 

• Delay timers (waiting before acting to avoid false positives) 

• Retry limits (how many times to attempt a recovery before giving up) 

Admins can also configure blacklists to prevent specific hosts or instances from being part of the recovery process—useful in maintenance or debugging scenarios. 

🧪 Masakari vs. Traditional HA Solutions 

You might wonder: why use Masakari instead of tools like Pacemaker, VMware HA, or proprietary clustering solutions? 

Here’s how Masakari stands out: 

• OpenStack-native: It integrates tightly with Nova and the OpenStack ecosystem. 

• API-driven: Fully RESTful, which means it's scriptable, automatable, and fits nicely into CI/CD pipelines. 

• Scalable and Flexible: Built for large cloud environments with thousands of VMs. 

• Policy-based: Fine-grained control over how failures are handled. 

However, unlike cluster-based HA solutions, Masakari doesn’t prevent failures—it simply reacts to them quickly and efficiently. It also focuses purely on instance availability, not application-level or database-level HA (which may require other tools). 

🔒 Security Considerations 

Because Masakari has the ability to reboot and move instances across the cloud, it's important to: 

• Use proper authentication via Keystone (OpenStack's identity service) 

• Secure its API endpoints 

• Set up role-based access controls so only authorized users or services can trigger recovery workflows 

💡 Use Cases for Masakari 

• Telecom clouds (NFV/ETSI environments) where availability is mission-critical 

• Financial services and banks needing strict uptime requirements 

• E-commerce platforms that can’t afford VM outages during peak traffic 

• Private enterprise clouds aiming for resilient infrastructure without relying on expensive vendor HA tools 

🌐 Final Thoughts 

Masakari is one of those tools that doesn’t get much spotlight, but quietly plays a crucial role in keeping cloud infrastructure reliable. If you're running OpenStack at scale and care about instance uptime, Masakari gives you the automation and intelligence to keep your workloads resilient—even when things go wrong. 

While it may not replace full-blown disaster recovery or application-level HA, it fills a critical gap in infrastructure-level fault tolerance, helping your cloud self-heal and reduce manual intervention. 

If high availability matters to your business, then Masakari should definitely be on your radar.