Scale Machine CPU and RAM

You can scale Machine memory and CPU settings for entire process groups in apps that are managed by Fly Launch (fly deploy + fly.toml). If you haven’t defined any process groups, then commands and settings are applied to all the Machines in your app (in the default app process group).

Machine size configuration precedence

1. The [[vm]] section in fly.toml: The fly deploy and fly scale count commands respect the VM size configurations in your app’s fly.toml file.
2. Existing Machine sizes in the app: If no VM size is set in fly.toml, then fly deploy won’t change existing Machines, and fly scale will use existing Machines to infer new Machine sizes.
3. Default Machine size of shared-cpu-1x: If no VM size is set in fly.toml, and there are no existing Machines to infer size from, then the default Machine size is used.

Check the VM resources on an app

Here’s a simple web app with three Machines running in different regions: two in Toronto and one in Tokyo. All the app’s Machines belong to the default process group, app, since no other processes exist.

fly status

App
  Name     = testrun                                        
  Owner    = personal                                   
  Hostname = testrun.fly.dev                                
  Image    = testrun:deployment-01GWZY7ZVJ2HNED4B0KZBPS3AQ  

Machines
PROCESS ID              VERSION REGION  STATE   ROLE    CHECKS                    LAST UPDATED
app     17811943f031d8  3       yyz     stopped         1 total, 1 passing          2024-02-07T15:34:57Z
app     328749d3c53958  3       yyz     stopped         1 total, 1 passing          2024-01-23T19:39:50Z
app     908057ef21e487  3       nrt     started         1 total, 1 passing          2024-01-23T19:39:51Z

fly scale show shows the CPU and RAM settings for all the Machines deployed using fly deploy under this app.

fly scale show

VM Resources for app: testrun

Groups
NAME    COUNT   KIND    CPUS    MEMORY  REGIONS    
app     3       shared  1       256 MB  nrt,yyz(2)

These Machines are running at the shared-cpu-1x preset scale, with a single shared vCPU and 256MB RAM.

Add Machine size configuration to fly.toml

With the [[vm]] section in fly.toml, you can set default Machine VM memory and CPU configurations, which take precedence when you run commands like fly deploy or fly scale count.

This example shows a very simple config that specifies the shared-cpu-2x preset with 2GB of RAM:

[[vm]]
  size = "shared-cpu-2x"
  memory = "2gb"

If you don’t include a process group in the [[vm]] section, then the settings apply to all process groups in your app. Add another [[vm]] section if you want different CPU or memory settings for specific process groups.

For details and more settings, see The vm section in the fly.toml reference.

Scale VM memory and CPU with flyctl

Use fly scale subcommands to apply VM memory and CPU settings to all Machines: fly scale vm applies a preset CPU/RAM combination; fly scale memory sets RAM separately, for cases when the preset’s RAM is not enough.

Select a preset CPU/RAM combination

There are a number of VM size presets available. See the list of valid named presets with fly platform vm-sizes.

Scale to a different preset using fly scale vm. In general, you should choose a named VM “size” based on your desired CPU type and scale; RAM can be increased separately.

fly scale vm shared-cpu-2x

Updating machine 148ed599c14189
  Waiting for 148ed599c14189 to become healthy (started, 1/1)
Machine 148ed599c14189 updated successfully!
Updating machine 32874400f35285
  Waiting for 32874400f35285 to become healthy (started, 1/1)
Machine 32874400f35285 updated successfully!
Updating machine 9080e6e1f94987
  Waiting for 9080e6e1f94987 to become healthy (started, 1/1)
Machine 9080e6e1f94987 updated successfully!
Scaled VM Type to 'shared-cpu-2x'
      CPU Cores: 2
         Memory: 512 MB

Check that the app process group has had this scale applied:

fly scale show   

VM Resources for app: testrun

Groups
NAME    COUNT   KIND    CPUS    MEMORY  REGIONS    
app     3       shared  2       512 MB  nrt,yyz(2)

You can also confirm that an individual Machine’s config matches this, using fly machine status <machine ID>:

fly machine status 148ed599c14189

Machine ID: 148ed599c14189
Instance ID: 01GX6Q2WE04M85XTHGPYGJK4X6
State: started

VM
  ...                                       
  Process Group = app                                        
  CPU Kind      = shared                                     
  vCPUs         = 2                                          
  Memory        = 512                                        
  ...

Looks good!

Add RAM

If you are happy with the provisioned CPU resources, but want more memory, then use fly scale memory to top up the RAM.

If your app crashes with an out-of-memory error, then scale up its RAM. Flyctl restarts the Machines to use the new setting. Scaling memory this way lets you test your app with more or less RAM, before optionally setting memory more permanently in fly.toml.

fly scale memory 4096

Updating machine 32874400f35285
  Waiting for 32874400f35285 to become healthy (started, 1/1)
Machine 32874400f35285 updated successfully!
Updating machine 148ed599c14189
  Waiting for 148ed599c14189 to become healthy (started, 1/1)
Machine 148ed599c14189 updated successfully!
Updating machine 9080e6e1f94987
  Waiting for 9080e6e1f94987 to become healthy (started, 1/1)
Machine 9080e6e1f94987 updated successfully!
Scaled VM Type to 'shared-cpu-2x'
      CPU Cores: 2
         Memory: 4096 MB

fly scale show

VM Resources for app: testrun

Groups
NAME    COUNT   KIND    CPUS    MEMORY  REGIONS    
app     3       shared  2       4096 MB nrt,yyz(2)

If you try to set an incompatible CPU/RAM combination through fly scale memory, flyctl will let you know. There’s a list of allowed CPU/RAM combinations and their prices on our Pricing page.

Scale by process group

Use the --process-group option to specify the process group to scale, with either fly scale vm or fly scale memory.

Here’s an app with two process groups defined:

fly scale show

VM Resources for app: mr18-2

Groups
NAME    COUNT   KIND    CPUS    MEMORY  REGIONS 
worker  2       shared  1       512 MB  ams,yyz
web     1       shared  1       512 MB  yyz   

Say the workers are constantly crunching data and need to be bigger. You can scale a single process group using the --process-group option:

fly scale vm performance-2x --process-group worker

Updating machine 0e286561f35586
No health checks found
Machine 0e286561f35586 updated successfully!
Updating machine 32873d9b012048
No health checks found
Machine 32873d9b012048 updated successfully!
Scaled VM Type for 'worker' to 'performance-2x'
      CPU Cores: 2
         Memory: 4096 MB

Check the result:

fly scale show

VM Resources for app: mr18-2

Groups
NAME    COUNT   KIND            CPUS    MEMORY  REGIONS 
worker  2       performance     2       4096 MB ams,yyz
web     1       shared          1       512 MB  yyz 

Machines not belonging to Fly Launch

If an app has Machines that don’t belong to Fly Launch (in other words, if you created Machines using fly machine run or the Machines API), then fly status will warn you of their existence:

Found machines that aren't part of Fly Launch, run fly machines list to see them.

The app-wide fly scale commands and any VM settings in fly.toml don’t apply to these Machines, but you can scale any Machine individually with fly machine update:

fly machine update --vm-size shared-cpu-2x 21781973f03e89
fly machine update --vm-memory 1024 21781973f03e89
fly machine update --vm-cpus 2 21781973f03e89

If you try to set an incompatible CPU/RAM combination through fly machine update --vm-memory or fly machine update --vm-cpus, flyctl will let you know. Learn more about individual Machine sizing with flyctl and the Machines API.