For a long time, I’ve intended to write this definitive guide, and now is the time to clarify the history, definition, and correct application of the “Pets vs. Cattle” meme. This analogy has become a cornerstone for understanding the paradigm shift to cloud computing. Its popularity stems from its ability to clearly differentiate between traditional and modern IT approaches. However, the meme’s effectiveness is diminished when misused or misinterpreted. In a landscape already cluttered with jargon like “cloud,” “hybrid,” and “DevOps,” precision is paramount. This article aims to provide a clear and authoritative account of the Pets vs. Cattle concept, ensuring everyone can use it accurately and effectively.
The Genesis of the Analogy
Around 2011 or 2012, I was grappling with the challenge of explaining to clients the fundamental differences between AWS, cloud-native applications, and cloud computing in general [1]. Traditional explanations were often lengthy and complex. I was searching for a concise way to encapsulate this paradigm shift when I stumbled upon a presentation by Bill Baker on Scaling SQL Server. It’s important to note that Bill wasn’t presenting this within cloud circles; I found it through diligent Google searching. His focus wasn’t specifically cloud computing, but rather the broader concepts of “scale-up” versus “scale-out” architectures.
Bill’s presentation used an analogy that immediately resonated with me: comparing scale-up and scale-out to the treatment of pets and a herd of cattle. A lightbulb went off in my head. This was the elevator pitch I had been searching for. However, I introduced a subtle yet crucial nuance. Firstly, I framed the pets vs. cattle analogy specifically within the context of cloud computing. Secondly, I emphasized the disposability of cattle and the irreplaceable nature of Pets. This distinction, I believed, was more fundamental than the scale-up versus scale-out debate. These scaling methods are, in my view, consequences of how you perceive a server. If you consider a server—whether physical, virtualized, or containerized—as something inherently replaceable and disposable, it belongs to the herd. Conversely, if you view a server (or a pair designed to function as a single unit) as indispensable, then it’s treated as a pet.
This led to the elevator pitch I frequently used in presentations, almost verbatim:
“In the traditional IT model, we treat our servers like pets, like ‘Bob’ the mail server. If Bob goes down, it’s an all-hands-on-deck emergency. The CEO can’t access email, and it’s a crisis. In the modern cloud approach, servers are treated as numbered cattle in a herd, like www001 to www100. When one server fails, it’s simply taken out back, metaphorically ‘shot,’ and automatically replaced in the line.”
This explanation of Pets vs. Cattle is what struck a chord with individuals like Tim Bell at CERN and countless others. They adopted and propagated the analogy, transforming it into a meme that has effectively educated many and clearly illustrated the ongoing transition to cloud computing.
Servers depicted as pets, emphasizing the intensive, individual care required in traditional IT environments.
Defining Pets and Cattle in Modern IT
To ensure clarity, let’s precisely define what we mean by “pets” and “cattle” in the context of server infrastructure.
Pets: Unique and Cherished Servers
Pets are servers or server pairs treated as indispensable, unique systems that must never experience downtime. They are typically manually configured, managed, and require constant “hand-feeding” – individual attention and care. Examples of pet servers include mainframes, standalone servers, high-availability (HA) load balancers/firewalls (active/active or active/passive setups), and database systems designed with a master/slave (active/passive) architecture. The focus is on maintaining these individual systems at all costs.
Cattle: Disposable and Scalable Infrastructure
Cattle represent server arrays consisting of more than two servers, provisioned using automated tools and designed to tolerate failures. In a cattle infrastructure, the loss of one, two, or even three servers is not considered catastrophic; no single server is irreplaceable. Ideally, failure events require minimal to no human intervention. The system is designed to “route around failures” by automatically restarting failed servers or replicating data through strategies like triple replication or erasure coding. Examples of cattle infrastructure include web server arrays, multi-master datastores like Cassandra clusters, clustered server racks, and any system that is load-balanced and multi-master in design.
The crucial distinction is that traditional redundancy, exemplified by the ubiquitous HA pair in enterprise data centers, is insufficient in the cloud era. The modern approach necessitates assuming that failures are inevitable and will occur. Every server, every component, must be designed to fail gracefully without disrupting the overall system’s functionality.
This pets vs. cattle analogy, as originally presented, has been instrumental in educating a generation of IT managers, CIOs, and other decision-makers. It provides them with a valuable tool for understanding and articulating the fundamental shift from traditional IT to modern, cloud-centric infrastructure.
Servers depicted as cattle, highlighting the automated management and scalability of modern cloud infrastructure.
The Misinterpretation and “Going Off the Ranch”
The core message of server disposability is essential to retain when using the Pets vs. Cattle analogy. While it’s natural for people to adapt and expand upon simple analogies, deviations can dilute the original, powerful message. Over time, the analogy has been extended and modified – examples include “pets, cattle, & ants” or “children, pets, and cattle.” While such adaptations might explore further nuances, they often obscure the initial clarity and impact of the core concept. A recent example illustrates this point.
The Kubernetes team, in a blog post titled Stateful Applications in Containers!? Kubernetes 1.3 Says “Yes!”, borrowed the Pets vs. Cattle analogy to introduce “Pet Sets” (now StatefulSets) to Kubernetes. It’s understandable that the container ecosystem might interpret the analogy in the context of stateful applications. Concerns around container applicability for stateful workloads have existed, perhaps due to earlier limitations in persistent storage support within container ecosystems. Projects like Rex-Ray emerged to address these challenges. However, this is a separate discussion.
The central issue with the Kubernetes blog post is its example applications for Pet Sets: “Cassandra, Kafka, and MongoDB.” These are textbook examples of cattle-architected data storage systems. They are inherently designed for failure and perfectly align with the “cattle” definition provided earlier. In essence, Kubernetes was promoting the use of “Pet Sets” for managing cattle data stores.
The problem arises from the implication that “Pet Sets” are also suitable for managing true “pet”-architected systems, such as active/passive Oracle databases or HA pairs of NFS file servers. While Pet Sets introduced features beneficial for managing stateful applications, including ordered deployment and stable network identities, they are fundamentally geared towards scale-out datastores – cattle – not traditional pets as originally defined.
This distinction is crucial. If we redefine “pets” to simply mean systems requiring “special handling” instead of systems that “cannot fail,” we risk confusing those seeking to understand the fundamental shift from the old IT paradigm to the new.
Preserving the Value of the Pets vs. Cattle Meme
Ultimately, the power of the Pets vs. Cattle analogy lies in its ability to quickly convey the core principles of modern, cloud-native infrastructure. While adaptations and reinterpretations are inevitable, it’s vital to remain grounded in the original message: the disposability and replaceability of servers. This concept, pioneered by companies like Google, is the cornerstone of cloud computing. Focusing on secondary aspects or misapplying the analogy—for example, equating stateful applications with pets—obscures this foundational shift.
If you choose to adapt the Pets vs. Cattle analogy for marketing or other purposes [2], it is your prerogative. However, understanding its original context and enduring value in educating IT professionals and executives about the fundamental changes in computing is essential. Attributing any new interpretations to this original source ensures clarity and preserves the meme’s educational power.
By accurately understanding and representing the origins of the Pets vs. Cattle meme, we maintain its value as a powerful tool for those navigating the ongoing disruption and foundational shift in how computing is delivered.
Cloud on.
[1] Referencing the Cloud Connect 2011 Keynote
[2] Expanding on this concept in The Rancher’s Dilemma: Reconciling Pets & Cattle
