Comparing EC2 and Lambda: A clear explanation of which to choose on AWS based on your needs.

Amazon Web Services (AWS)When building processing infrastructure or applications, EC2 and Lambda are often mentioned as points of comparison. Both are services for executing code, but their mechanisms, operational approaches, and suitable applications are different.

The important thing is not to choose based on simplistic understandings like "EC2 is for flexible configuration" or "Lambda is for serverless." The appropriate choice will vary depending on processing time, access fluctuations, operational structure, and the required degree of flexibility.

This article will explain the differences between EC2 and Lambda, making it easier to decide which to choose in different situations.

What are the differences between EC2 and Lambda?

EC2 and Lambda are often compared as ways to run code on AWS. However, although both are "services that run processes," their design premises are quite different.

• EC2
  • This service launches a virtual server and runs applications and middleware on it. It's similar to setting up your own server and configuring the OS and execution environment yourself.
• Lambda
  • This service doesn't keep the server running constantly; instead, it executes only the necessary processes when needed. It's well-suited for use cases where you want to run code triggered by events such as file uploads or API requests.

The differences aren't just in the execution method. There are also differences in ease of operation, billing methods, and suitable applications.

EC2 is a virtual server-type execution environment.

EC2 is a service that allows you to launch and use virtual servers on AWS. Users select an instance with the necessary CPU and memory, and then run the OS, middleware, and applications on it.

While you don't need to provide your own physical servers, the approach is similar to traditional server management. You can decide which OS to use, which software to install, and how to configure security. This offers a high degree of freedom, but it also means that the responsibility for setup and maintenance remains with the user.

For example, EC2 is more suitable for business systems that run continuously for long periods of time, or applications that require a unique middleware configuration. It's also an easy service to choose when you want to migrate your existing server configuration to the cloud as is.

Lambda is an event-driven execution environment.

Lambda is a service that executes code in response to specific events. Unlike EC2, which requires a virtual server to run continuously, Lambda automatically executes only when processing is needed.

For example, typical processes include converting images when files are uploaded to S3, sending notifications after form submissions, and responding to requests via APIs. It has the advantage of easily separating code into processing units and running only when necessary, thus reducing the load on server operation.

On the other hand, it's not suitable for all types of processing. It's not ideal for systems that require long processing times or constant operation, or for cases where you want fine-grained control over the OS or execution environment.

A comparison of the differences between EC2 and Lambda in a list.

If you prioritize flexibility, choose EC2; if you prioritize low operational burden, choose Lambda.

However, in actual selection, this alone should not be the sole deciding factor. You need to consider processing time, whether continuous operation is required, fluctuations in access, and the degree of flexibility required for the execution environment before making a decision.

The main differences between EC2 and Lambda

When comparing EC2 and Lambda, you need to consider not only the execution method, but also billing, operational burden, scaling, and flexibility.

Differences in billing methods

EC2 on-demand pricing is based on the number of seconds an instance is running. The minimum usage time is 60 seconds. Even if there is idle time when no processing is being done, costs are incurred as long as the instance is running. Therefore, it is a service that is easy to estimate for systems that run continuously or workloads with a constant load.

Lambda, on the other hand, charges based on the number of requests and execution time. It is well-suited to configurations that execute processing only when needed, and is characterized by low waiting costs for processes that run only during off-peak hours or when events occur.

However, Lambda isn't always the cheapest option. While it's efficient for short, intermittent processes, it can become costly for frequent or longer-running tasks. The billing model should be considered not just in terms of the unit price, but also in terms of whether it aligns with your processing patterns.

Differences between operation and maintenance

With EC2, you need to consider OS management, patching, middleware updates, monitoring, and incident response. While AWS manages the physical infrastructure, making it less burdensome than on-premises environments, the scope of responsibility for the user is still broader.

Lambda is a service that helps reduce the burden of infrastructure operations because it can be used without having to worry about server setup or OS management. Since you don't have to assume instance survival management or OS maintenance, you can focus more on application development.

However, Lambda still requires operational management. Detecting execution failures, handling retries, and checking logs must all be designed in advance. EC2 instances tend to involve more server management, while Lambda reduces server management but requires operational design specifically for event processing.

Scaling differences

EC2 requires a design that adjusts the number and specifications of instances according to the load. While Auto Scaling can automate this process, you need to decide in advance under what conditions to increase or decrease instances, and how much headroom to maintain.

Lambda is a service that scales easily and automatically in response to requests and events. However, it needs to be designed with concurrency quotas and per-function scaling speeds in mind. This characteristic is particularly useful for processes that usually have low loads but experience sudden spikes in access during specific times or events.

However, Lambda is not unlimited in its usage. If you don't consider the number of concurrent executions and the design of the connections, other parts of the system will become bottlenecks. It's helpful to think of EC2 as a service where you design the scale yourself, while Lambda is a service designed with the assumption that it will automatically increase.

Differences in execution time and configuration constraints

Because EC2 runs on virtual servers, it's a service that can easily handle long-running processes and is well-suited for configurations that run persistent processes. It's particularly well-suited for processes that run continuously in the background or batch processes that require a significant amount of time.

Lambda, on the other hand, is a service designed for processing that is completed in a short amount of time. It is suitable for use cases where it is executed in response to an event and terminates when it is finished, but it is not suitable for applications that require continuous operation over long periods of time. It will likely have limitations when it is necessary to run it continuously or when processing that needs to maintain a state.

Therefore, whether the processing can be broken down into short segments or whether continuous operation is required are major factors in deciding whether to use EC2 or Lambda. Choosing Lambda without clarifying these points can easily lead to design problems.

Differences in customizability and degree of freedom

EC2 is a highly flexible service because you can design everything yourself, including the OS and execution environment. Because you have broad control over the middleware, settings, libraries, and configuration used, it's easier to accommodate adjustments to existing systems or requirements that don't fit within standard configurations.

Lambda is an execution service that allows you to use custom runtimes and container images in addition to the runtimes provided by AWS. On the other hand, it does not allow for continuous control of the OS or persistent processes, so EC2 offers greater flexibility in the execution environment.

If you want to meticulously create your own unique configuration, EC2 is suitable. Conversely, if you prioritize running the process simply over the details of the execution environment, Lambda is a better fit.

Cases where EC2 is suitable

EC2 is suitable when you need to keep the server running continuously or when you want to design the execution environment in detail. For requirements that are difficult to handle with Lambda, which only runs processes when needed, EC2 is easier to configure.

A system that runs for extended periods

EC2 is suitable for systems that require continuous processing over long periods of time.

For example, web servers that constantly receive requests, business systems that run continuously, and batches that perform heavy processing at regular intervals are easier to handle with EC2 than with Lambda, which is designed for short-term execution.

Because EC2 uses virtual servers that are already running, it's easier to design them with long processing times in mind, and continuous operation itself doesn't seem unnatural. Conversely, Lambda is well-suited for processing that can be broken down into short segments, and is not suitable for applications that require processing to run continuously for long periods.

If the process won't finish immediately, or if you need to keep it running for a certain period of time until it finishes, then it's practical to start by considering EC2 as the main solution.

If you want to have fine control over the OS and middleware

EC2 is also suitable if you want to fine-tune the execution environment.

With EC2, you can choose the operating system, middleware, runtime, and configuration settings yourself. Because you can flexibly design which software to install and how to run it, it's easier to address requirements that don't fit into standard configurations.

For example, in systems that rely on a specific middleware configuration or applications that require fine-tuning, this flexibility translates to ease of use. While Lambda can implement certain features to some extent, EC2 is more suitable if you want broader control over the execution environment itself.

If you want to migrate your existing server configuration as is

EC2 is an easy service to choose if you want to migrate your existing on-premises or virtual server environment to the cloud.

Some existing systems run resident processes on servers or rely on specific OS settings or middleware configurations. If you want to migrate without significantly changing these configurations, EC2, a server-based execution environment, is a more suitable option.

Migrating to Lambda requires breaking down processes into event-based units or reviewing the entire configuration. While this isn't inherently bad, it can be a significant burden when you want to leverage existing assets as much as possible.

If your primary goal is to stably migrate your current system to the cloud, EC2 is a more practical option.

Applications designed for continuous operation

EC2 is also suitable if the application itself is designed to run continuously.

For example, for web applications that need to be constantly listening for connections, or services that continuously receive connections, it's more natural to design them assuming the server is always running. EC2 makes it easier to run applications while instances are continuously running, thus facilitating this kind of configuration.

Lambda's strength lies in its ability to run only when needed, but it's not well-suited for designs that require continuous operation. While it's well-suited for event-driven automation, it's often not ideal for directly replacing persistent applications.

If you need to keep your application running continuously, choosing EC2 is the more natural option.

Cases where Lambda is suitable

Lambda is suitable for situations where processing doesn't need to be running constantly, but only when necessary. In cases where you want to structure processing on an event-by-event basis, rather than relying on setting up and maintaining a server like with EC2, Lambda is easier to handle.

If you want to run a process only when an event occurs

If you only want to execute a process when a certain event occurs, Lambda is a strong option.

For example, in cases such as converting images when files are uploaded to S3, sending emails or notifications after form submissions, or running scheduled processes, it's not necessary to keep the server running constantly. A configuration where processes start when needed and stop when finished is more natural.

While the same process can be implemented on EC2, maintaining a server for that purpose tends to result in a somewhat heavy design. If the starting point of the process is clear and it is easy to complete independently each time it is executed, Lambda allows for a simpler configuration.

When the number of accesses fluctuates significantly

Lambda is a user-friendly service even for processes with large fluctuations in access numbers and execution frequency.

For example, for APIs that normally receive few requests but see a sudden surge during campaigns or specific time periods, or processes where events occur in batches at specific times, having a server with ample capacity at all times can easily lead to wasted resources.

Lambda is well-suited to these kinds of fluctuating workloads because it scales automatically as needed. However, during surges, you need to design your system to account for concurrency quotas and connection constraints. In configurations where it's mostly inactive and only runs when needed, the advantage is that it minimizes the need for idle resources.

Of course, this doesn't mean you can ignore the simultaneous execution during surges or the load on the connected servers. However, if you want to reduce the burden of having to consider the number of servers in response to increases and decreases in access, Lambda is often a more suitable choice.

When you want to quickly implement a small feature

Lambda is also suitable when you want to quickly implement a function that is small in scale and focused on a single role.

For example, functions such as receiving and formatting data, notifying external services, validating input, and calling other processes under specific conditions are typical examples of functions that are easy to extract into a single function. Sometimes, implementing only the necessary processes independently, rather than putting the entire application on a large server, can speed up development and modification.

This property is effective not only for new development but also when you want to automate a part of an existing system. It's also a user-friendly configuration for when you want to try out small processes before building a large system.

If you want to reduce the load on server operations

Lambda is also a viable option if you want to minimize the effort involved in server management.

With EC2, you need to consider instance management, OS and middleware updates, monitoring, and handling failures. On the other hand, with Lambda, there is no premise of directly managing virtual servers, so the operational costs of maintaining servers can be significantly reduced.

This difference is particularly important when you want to operate with a small team or when you want to focus on application development rather than infrastructure management. The ease of managing each process as a function and the reduced time spent on infrastructure maintenance are likely reasons to choose Lambda.

However, this doesn't mean that operations will be completely eliminated. In addition to checking logs, designing retry procedures in case of failure, monitoring, and setting permissions, if using event sources, you need to consider idempotency assuming duplicate executions. Even so, if you don't want to take on the responsibility of OS and server maintenance, Lambda is lighter and easier to manage than EC2.

Key points to consider when deciding between EC2 and Lambda.

When choosing between EC2 and Lambda, you should consider factors such as processing time, whether continuous operation is required, how to handle fluctuations in access, the effort you can dedicate to operation, and the degree of flexibility you require in the execution environment. Lambda has limitations on execution time and the number of concurrent executions, while EC2 allows you to design the number of instances and performance yourself. Based on these differences, you need to choose the one that best suits your company's requirements.

Will the process be completed in a short time?

The first thing to check is whether the process can be completed in a short amount of time. Lambda can run for up to 15 minutes, but it is not suitable for long-running processes or processes that require continuous background operation. Lambda is a good fit for processes that can be completed independently each time, such as file conversion, notifications, and API request processing.

Conversely, for batches that run for extended periods or processes that maintain state, EC2 is easier to handle.

Is it necessary to keep it running at all times?

Whether the application or process needs to be running constantly is also a factor to consider. EC2 can be used with the assumption that instances will remain running, making it suitable for web applications that are constantly listening and services that run continuously.

Lambda functions are invoked only when needed. They are suitable if you don't need to maintain a waiting state and only need to process an event the moment it occurs, but they are not suitable for designs that require continuous operation.

To what extent do you want to automatically handle fluctuations in traffic?

How you want to handle fluctuations in access and execution volume is also an important factor in selection. Lambda is well-suited for processes that have low loads under normal circumstances but experience sudden spikes in access during specific time periods, as it can easily increase execution volume in response to increased requests.

While EC2 instances can also be automated with Auto Scaling, you have to design the thresholds, minimum and maximum number of instances, and health checks yourself. If you want to finely control the rate of growth or ensure a constant level of processing power, EC2 is easier to handle.

How much effort can be put into infrastructure operations?

The amount of time and manpower that can be dedicated to operations is also a factor that influences the selection. With EC2, operations such as OS management, patching, middleware updates, monitoring, and incident response are required to maintain the server.

With Lambda, you don't need to manage the server itself; the focus shifts to the code, execution settings, logs, permissions, and how to handle failures. Lambda is often a better fit for small teams or when you want to concentrate on application development rather than infrastructure maintenance. However, even with Lambda, monitoring, retry design, and error handling are still necessary.

How much flexibility is needed in the execution environment?

The final thing to consider is how much freedom you want to have in designing your execution environment. EC2 offers broad control over the OS and middleware, making it a service that easily adapts to existing systems and allows for custom configurations.

In contrast, Lambda is fundamentally based on the idea of ​​running code within a pre-defined execution environment, although memory, ephemeral storage (/tmp), and runtime management settings can be adjusted. However, it doesn't offer the same level of flexibility regarding the OS and persistent requirements as EC2.

If you need to meticulously customize the execution environment, EC2 is suitable, but if you prioritize simple processing over environment flexibility, Lambda is a better choice.

Summary

The difference between EC2 and Lambda is not simply a difference in services, but rather a difference in how processing is executed and the underlying operational assumptions. EC2 is suitable for processes that need to run for a long time, applications that run continuously, and when you want to design the execution environment in detail.

Conversely, if you want to trigger short-term processing in response to an event, execute tasks flexibly in response to fluctuations in access, or reduce the burden on server operation, Lambda is a suitable option.

The deciding factors should not be the impression the service name gives, but rather the processing time, whether it needs to be running continuously, fluctuations in access, the operational structure, and the degree of flexibility in the execution environment. Organizing the requirements in this order will make it easier to determine which is the more natural choice.