One question I hear a lot lately is when a company should stick with Heroku or switch to something else. In this article I'm going to lay out the pros and cons for Heroku, and compare it with the typical alternative, AWS.

Three reasons to stick with Heroku

Don't fall victim to thinking that "the grass is always greener on the other side." That hot new technology on AWS or Azure may look cool now, but Heroku offers a lot of great features that should fit the bill for many growing companies.

Heroku supports easy scaling with sticky sessions

Horizontally scaling any web application is hard. In a traditional web app, you must optimize your code so that it runs in parallel. You must deal with race conditions that arise when multiple servers are trying to interact with a shared resource such as a cache or a database. You must find a way to balance load across multiple servers while sharing state across all instances.

Session data is visitor-specific data that is stored on the server. If a visitors's session is stored on one server, but their request is routed to another server, then that server won't know about anything they've done in the current session. It may not know if they're logged in or not. It may not have the browsing filters that they've configured.

Session affinity, also known as sticky sessions, is one solution to the problem of sharing session across servers. With session affinity enabled, all of a visitor's requests will always be routed to the same instance. There are some drawbacks to session affinity, but the benefit of being able to scale horizontally before having to tackle some parallelization problems may outweigh the drawbacks in your use case.

Many services offer session affinity, but none are as easy to set up as Heroku. With literally two clicks you can enable session affinity and start scaling out. Don't let hype distract you from an approach that may reap benefits for your web property.

Heroku provides zero down time deploys and upgrades

One of the best features of Heroku is that their technology and support teams handle deploys and upgrades. They make it so that your dev team doesn't have to worry about keeping the servers up during deploys or running migrations during upgrades.

The preboot feature allows you to keep the old version of your app running during a deploy. This means that users will only ever be routed to a server that has booted up and is running your app, and that means that you aren't turning away customers in that 30 second window where the new version of your app is loading.

Heroku also supports seamless upgrades for the most popular add-ons, such as REDIS. When I switched my company from Heroku REDIS to AWS REDIS we were surprised that our site went down a few weeks after the switch. AWS may force upgrade your technology without providing a way to seamlessly switch to the new version. So AWS forces you to track each upcoming patch and ensure that your team is ready for the switch.

Heroku is cheaper than the alternative because anyone can use it

Heroku seems very expensive when the bills come due, but in my experience it's cheaper than the alternative. Heroku is so easy to use that anyone can use it. With a few clicks or commands a backend developer can enable sticky sessions. With a few clicks or commands they can enable preboot. With a few clicks or commands they can add REDIS or PostGreSQL or any of the many add-ons provided by Heroku.

To use all those different products on a less managed product, such as AWS or Azure, you must retain a dedicated DevOps specialist. These people have very specialized skills and are not cheap. In my experience, using Heroku saves the cost of around one expensive employee. So as long as your Heroku bill is less than the cost of one employee, it's probably the more affordable option.

Three reasons to switch

There are many good reasons to stick with Heroku, but it certainly has limits. Here are the reasons why I've moved services from Heroku to somewhere else in the past.

Heroku is dangerous because anyone can use it

When you're on Heroku, you may not need to hire dedicated staff to manage your web infrastructure. This is a significant cost savings, but it means that the DevOps tasks are going to be offloaded on your web programmers. So you must ensure that you hire the skills on your team to understand Heroku. Heroku may not be as complex as AWS, but it still requires a foundational understanding of how the web works, linux, and logging. If your programmers are exploring the features in Heroku without the requisite experience or training then they may make mistakes that harm your business.

Heroku offers fewer options for international support

Heroku lacks flexible support for internationalized websites. As it says in the regions documentation, each "Private Space exists in a single region, and all applications in the Private Space run in that region.". This may sound confusing, but it ultimately means that each project in Heroku can only run in one region. If you want to support another region, then it must be in a separate project and hosted at a separate domain or subdomain. So if you want to internationalize your website using subdirectories, which is advantageous because it inherits the existing search reputation of your domain, then you can't do that with geographically distributed servers on Heroku.

Heroku offers fewer vertical scaling options

Heroku dynos come in six different flavors as of this writing. If you need anything outside of those six options then you are out of luck. The beefiest dyno is the performance-l machine, which offers 14Gb of RAM. If you need more than that, then you need to switch to another platform. What if you're using very little memory, but you want to use many CPU cores? The only option is to pay for the most expensive dynos. This lack of flexibility means that if your web service is a pretty standard website or API, then Heroku probably won't serve your needs very well.

How to decide whether to stick with Heroku or to switch

In this article I've listed some reasons to stick with Heroku and some reasons to switch, but the final decision is largely dependent on your use case. If you are making a pretty standard website or API, then Heroku is probably fine even when horizontally scaling. There are three main scenarios where you should strongly consider switching to a more complex cloud hosting service.

1. Your service need more flexible options for internationalization
2. Your service doesn't match the requirements common to most web apps and APIs
3. Your service is scaling exponentially