The “Pets vs Cattle” analogy has become a cornerstone in explaining the fundamental shift in how we approach server management, particularly in the realm of cloud computing. For years, this concept has effectively illustrated the difference between traditional IT infrastructure and the modern, cloud-native approach. This article aims to provide a definitive explanation of the Pets vs Cattle meme, ensuring its accurate understanding and continued value in the ever-evolving tech landscape, particularly for those new to cloud concepts and the nuances of managing Pets And Pet projects within it.
The Genesis of the Analogy
Around 2011 or 2012, the challenge was to articulate the paradigm shift brought about by AWS, cloud-native applications, and cloud computing in general. Traditional explanations were often lengthy and complex. The search for a concise and impactful way to convey this difference led to an insightful presentation by Bill Baker on Scaling SQL Server. While Bill’s presentation wasn’t directly about cloud, his discussion of “scale-up” versus “scale-out” architectures, using the pet and cattle analogy, sparked a crucial insight.
Bill’s analogy of pets and cattle, used to differentiate scale-up and scale-out strategies, resonated deeply. It became clear that this was the concise explanation needed to encapsulate the essence of the cloud revolution. However, to make it directly relevant to cloud, two key nuances were emphasized: first, framing pets vs cattle within the context of cloud computing, and second, highlighting the disposability of cattle and the irreplaceable nature of pets. This distinction went beyond just scaling strategies; it touched upon the fundamental philosophy of server management. The perception of a server – whether physical, virtualized, or containerized – as disposable and replaceable defines it as “cattle”. Conversely, viewing a server as indispensable, requiring special care and manual intervention, categorizes it as a “pet”.
This led to the development of a concise elevator pitch, used in presentations to effectively communicate this concept:
In traditional IT, servers are often treated like pets, each with a name and unique identity, such as “Bob, the mail server.” If Bob encounters issues, it’s an emergency, requiring immediate and dedicated attention. In the modern cloud approach, servers are treated as cattle, identified by numbers, like “webserver001 to webserver100.” If one server fails, it’s simply taken offline and automatically replaced, with minimal disruption.
This explanation of Pets vs Cattle resonated widely, including with Tim Bell at CERN, and became a powerful meme, effectively illustrating the transition to cloud computing and the different approaches to managing infrastructure, especially when considering the life cycle of pets and pet projects within organizations.
Defining Pets and Cattle in Detail
To ensure clarity, let’s delve deeper into the definitions of pets and cattle in the context of server management and cloud computing.
Pets: The Indispensable Servers
Pets are servers or server pairs considered unique and indispensable. They are often manually configured, meticulously managed, and require individual attention – much like caring for a pet. Downtime for a pet server is unacceptable and considered a critical incident. Examples of pet servers include mainframes, standalone servers, high-availability (HA) load balancers or firewalls in active/active or active/passive configurations, and master/slave database systems. These systems are often built with the expectation of longevity and are nurtured to ensure continuous operation, reflecting the personalized care given to pets.
Alt text: IT professionals lovingly tending to servers as if they were pets, symbolizing traditional server management.
Cattle: The Disposable Infrastructure
Cattle represent servers in arrays of more than two, built using automated tools and designed with failure in mind. In a cattle infrastructure, individual servers are replaceable and not considered critical. Automated systems handle failures, often without human intervention, by routing around issues, restarting failed instances, or replicating data through strategies like triple replication or erasure coding. Examples of cattle infrastructure include web server farms, multi-master datastores like Cassandra clusters, and clustered server racks. These systems are designed for resilience through redundancy and automation, mirroring the management of a herd of cattle where individual animals are less critical than the overall herd’s health.
The critical distinction lies in the approach to redundancy and failure. The traditional “pet” model relies on having pairs of everything for high availability, a common practice in enterprise data centers. However, the “cattle” model embraces the inevitability of failure. It assumes that any server or component can fail at any time and designs the system to withstand such failures without significant impact. This shift in mindset is crucial for understanding the benefits of cloud computing and managing infrastructure at scale, moving away from the intensive care of individual pets to the automated management of cattle.
Straying from the Core Message
The power of the Pets vs Cattle analogy lies in its simplicity and clarity. However, like any successful meme, it has been adapted and modified for various contexts. While some adaptations can be insightful, others dilute the core message and create confusion. It’s important to understand the original intent to appreciate its true value, especially when considering the management of pets and pet projects within a larger “cattle” infrastructure.
For example, the Kubernetes team adopted the analogy to introduce “Pet Sets” (now StatefulSets) in Kubernetes 1.3, as explained in their blog post Stateful Applications in Containers!? Kubernetes 1.3 Says “Yes!”. While understandable in the context of container ecosystems and the initial concerns around stateful applications in containers, this interpretation somewhat misrepresents the original analogy. The Kubernetes blog used Pets vs Cattle to differentiate stateful applications (pets) from stateless applications (cattle) in containers.
However, the examples of “stateful applications” supported by Kubernetes Pet Sets – Cassandra, Kafka, and MongoDB – are fundamentally cattle-architected systems. These are distributed data stores designed for failure and scale-out, precisely aligning with the definition of cattle. Therefore, Kubernetes Pet Sets, in reality, were designed to better manage cattle-style data stores within containers, not truly “pet” systems like single-instance databases or traditional HA pairs.
Alt text: Rancher efficiently managing a herd of cattle, symbolizing scalable and automated server management in cloud environments.
This reinterpretation, while perhaps serving the purpose of highlighting stateful application support in Kubernetes, can lead to confusion. It implies that Pet Sets are for managing systems requiring “special handling” (pets in the Kubernetes context), rather than reinforcing the original message about disposable infrastructure (cattle). This subtle shift can muddy the waters for those trying to grasp the fundamental difference between the old and new paradigms of IT infrastructure management, particularly when considering the lifecycle of pets and pet projects in a cloud-native environment.
Maximizing the Value of Pets vs Cattle
While adapting the Pets vs Cattle analogy for different purposes is inevitable, it’s crucial to remain grounded in its original meaning to retain its educational value. If you choose to reinterpret it for marketing or other purposes, acknowledging the original context and referencing its history is highly recommended. Understanding the meme’s origin ensures its continued effectiveness in helping IT professionals and executives understand the profound shift in computing.
Ultimately, the most crucial aspect of the Pets vs Cattle analogy is the concept of server disposability – a principle pioneered by Google. Focusing on this core idea allows for a clear understanding of the transformative shift in how computing infrastructure is designed and managed. Diluting this message by emphasizing secondary aspects or misattributing characteristics (like associating stateful applications with pets in the original analogy context) diminishes its impact and creates unnecessary confusion.
By accurately understanding and representing the origins of the Pets vs Cattle meme, we preserve its power to educate and guide those navigating the ongoing evolution of cloud computing. It remains a vital tool for quickly grasping the foundational changes in how technology is delivered and managed, and for understanding the strategic choices between managing pets and building cattle-like infrastructure for modern applications and services.
Cloud On.
