High memory usage in deployed Next.js project

I have been working on a small project to reproduce an issue related to memory usage in Next.js. The project is built using the Next.js canary version 13.4.3-canary.1. It utilizes Next.js with App Router and Server Actions and does not use a database.

The problem arises when deploying the project on different platforms and observing the memory usage behavior. I have deployed the project on multiple platforms for testing purposes, including Vercel and Fly.io.

  • On Vercel: https://next-js-ram-example.vercel.app/
    When interacting with the deployed version on Vercel, the project responds as expected. The memory usage remains stable and does not show any significant increase or latency
  • On Fly.io: https://memory-test.fly.dev/
    However, when deploying the project on Fly.io, I noticed that the memory usage constantly remains around 220 MB, even during normal usage scenarios. Furthermore, when interacting with the project by clicking on the navigation bar to switch between different pages, it appears unresponsive and fails to provide the expected response or navigate smoothly.

I expect the small project to run smoothly without encountering any memory-related issues when deployed on Fly.io. Considering the previous successful deployment on Fly.io, which involved additional resource usage and utilized Next.js 13 with App Router and Server Actions, my anticipation is that the memory usage will remain stable and within acceptable limits.

Vercel/Next.js Issue: High memory usage in deployed Next.js project · Issue #49929 · vercel/next.js · GitHub
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This seems like expected behavior. V8 will typically use as much memory as you allow it to use. Unless you see memory errors or bad performance I wouldn’t worry about it.

See this comment by Matteo Collina from the Node TC and main author of Fastify, Undici, etc:

Something else to consider is that when running a Next app in Vercel, it’s executed with AWS Lambda. It’s a very different environment than Node running in a VM.

Honestly, it wouldn’t surprise me if Next had a memory leak in Node since it’s optimized for Vercel. Wouldn’t be the first time.

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Thank you for your response and the information provided. Unfortunately, I’m still experiencing an issue with memory usage when deploying the project on Fly.io. Despite my previous successful deployment on Fly.io using additional resources and an earlier version of Next.js, the project continues to encounter high memory usage and eventually gets killed due to running out of memory. This issue is preventing the project from running smoothly on the platform.

Here’s an excerpt from the recent logs:

2023-05-24T11:57:16.113 app[6e82dd75c45d87] arn [info] [ 354.343753] Out of memory: Killed process 513 (node) total-vm:803956kB, anon-rss:54272kB, file-rss:4kB, shmem-rss:0kB, UID:0 pgtables:1140kB oom_score_adj:0

2023-05-24T11:57:16.313 app[6e82dd75c45d87] arn [info] Starting clean up.

2023-05-24T11:57:16.313 app[6e82dd75c45d87] arn [info] Process appears to have been OOM killed!

2023-05-24T11:57:17.313 app[6e82dd75c45d87] arn [info] [ 355.545338] reboot: Restarting system

2023-05-24T11:57:17.410 app[6e82dd75c45d87] arn [info] Out of memory: Killed process

2023-05-24T11:57:17.458 runner[6e82dd75c45d87] arn [info] machine did not have a restart policy, defaulting to restart

In the issue I created on the Next.js GitHub repository (#49929), I received a response suggesting that this behavior might be related to a memory leak. Here is the comment in question.

This information further supports the observation that there might be a memory-related issue causing the high memory usage and unresponsiveness in the project when deployed on Fly.io.

I would greatly appreciate any further insights or suggestions on how to address this memory issue and ensure the project runs smoothly on Fly.io.

Thank you for your assistance.

I would like to add here that the amount of RAM coming from fly machine status id-xxx-xxx-xx is not the same you would have available in the system. If you inspect the operative ram runing grep MemTotal /proc/meminfo being connected via flyctl ssh console:

➜  next-js-app:(main) ✗ flyctl ssh console
Connecting to xxx:0:xxx:a7b:23:sss:xxx:2... complete
xxxx12xxx12xxx:/app# grep MemTotal /proc/meminfo
MemTotal:         225996 kB

So if your machine has 256MB from the free allowance your app should run under 225MB. I am not sure If this behaviour is new. but recently all my Next.js apps in free allowances are way slower than usual.

This can be of course a Next.js leak but also maybe the amount of operative RAM being less than the advertised.

@jerome @shortdiv would it be possible to get an official Fly.io team response to these memory problems? Deploying an app with the current Next.js version to a Hobby plan machine now currently leads it continuously crashing.

Also - has the default amount of memory changed from 256MB to 225MB like @josehower mentioned above?

Hey there,

According to the issue on the next.js repo, there’s a memory leak from the event emitter. I bet most people run their next.js apps in serverless environment where they’re short-lived and recycled before they hit these issues? I’m not certain.

Can you try adding some swap memory to your machine until this is resolved upstream? Here’s a simple way to do it: Swap memory - #2 by OldhamMade

Adding swap won’t exactly help forever if there is a memory leak, it’ll just take longer before it runs out of memory.

As mentioned before, since Vercel runs on AWS Lambda, there are many differences, including the fact that the virtual machines are constantly being stopped and started, preventing the accumulation of leaked memory.

Looking at the next.js repository, there are a lot of memory leak issues, often without resolution / response.

I looked at apps v1 platform VMs and they seem to have the same discrepancy. I’m looking around a bit, but I’m not sure where it comes from. We’re passing in 256MiB to firecracker, I am sure of that. So the discrepancy is created somewhere else, either from firecracker or the kernel? Not sure.

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Ok, seems like this is normal. Here’s a line from the kernel messages boot log:

# free -m
               total        used        free      shared  buff/cache   available
Mem:             221          26          74          10         120         176
Swap:              0           0           0
# dmesg | grep Memory:
[    0.006260] Memory: 203120K/261752K available (12295K kernel code, 8279K rwdata, 5492K rodata, 1792K init, 6196K bss, 58376K reserved, 0K cma-reserved)

Looks like the total memory is correct here: 261752K / 1024 = ~256MiB

The “missing” memory is reserved by various kernel things (see the kernel code, rwdata, etc. in that log line). We are running full virtual machines after all, there is some overhead involved within a machine.

Thanks for the tip about swap memory - I talked with @josehower offline and he mentioned that he’s going to give this a shot next week, and report the findings back here

Thanks for the tip about swap memory - I talked with @josehower offline and he mentioned that he’s going to give this a shot next week, and report the findings back here

Ah double-posted, sorry about that, tried to delete the extra post but I guess this community software (I think Discourse) doesn’t allow deletions without leaving some trace behind :grimacing:

As a follow up. @josehower tried to add the Swap memory procedure but this really didn’t change much the behaviour.

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