Scale V1 (Nomad) Apps
There are multiple dimensions of scaling on Fly.io.
- Ensuring the application has instances running in one or more regions
- Increasing the CPU cores and memory size of application instances
- Alternate scaling models with autoscaling
Regions and Scaling
Your Fly application runs on servers in a pool of regions, selected from our available regions. That pool, which you can configure, represents the regions your app can be deployed in.
When you deploy an application for the first time, we pick a first region to deploy in. Our selections are simple:
- If you’re turbo-charging a Heroku application, we pick regions close to the Heroku application (currently, this means
iadfor US Heroku applications (howdy!), and
amsfor European applications (hallo!).
- Otherwise, you're prompted to select an initial region when you run
You can confirm this by running
fly regions list.
fly regions list
Region Pool: lhr Backup Region:
The create command, in this case, was issued in the UK, so London (LHR-London Heathrow) is the closest region.
Continuing our previous example: if for any reason your application can't be deployed in LHR, Fly will attempt to bring it up in either
ams (Amsterdam) or
fra (Frankfurt). Users won't notice this! They’re directed to the nearest running instance automatically. Backup Regions are selected based on the geographical closeness of the regions selected for your region pool.
Modifying the Region Pool
You can build your own region pool easily.
fly regions add ord iadadds
iadto your region pool.
fly regions remove ordremoves
ordfrom your region pool.
Both commands simply take a space-separated list of regions to add or remove.
Now that we have control over where our application runs, we can talk about how many instances of your app are running.
Your application has a “scale count”. The scale count defaults to 1, meaning 1 instance of your application runs on Fly, in one of the regions in your pool.
If you want to run more than 1 instance, change your scale count with the
fly scale count command.
fly scale count 3 tells us to run 3 instances of your application.
When you bump up your scale count, we’ll place your app in different regions (based on your region pool). If there are three regions in the pool and the count is set to six, there will be two app instances in each region.
You can see your current scaling parameters with
fly scale show.
fly scale show
VM Size: shared-cpu-1x VM Memory: 512 MB Count: 4
This application uses the shared-cpu-1x (one shared CPU) VM size, with 512MB of RAM for each instance and there should be four instances of it created.
Scaling Virtual Machines
Each application instance on Fly runs in a virtual machine. The number of cores and amount of memory available in the virtual machine can be set for all application instances using the
fly scale vm command.
Viewing the Current VM Size
fly scale show on its own will display the details of the application's current VM sizing.
fly scale show
Size: shared-cpu-1x CPU Cores: 1 Memory: 256 MB Max Per Region:
It shows the size (
shared-cpu-1x), number of CPUs, and memory (in GB or MB).
Viewing Available VM Sizes
fly platform vm-sizes command will display the various sizes with cores and memory:
fly platform vm-sizes
NAME CPU CORES MEMORY shared-cpu-1x 1 256 MB dedicated-cpu-1x 1 2 GB dedicated-cpu-2x 2 4 GB dedicated-cpu-4x 4 8 GB dedicated-cpu-8x 8 16 GB
The CPU Cores column shows how many vCPU cores will be allocated to the virtual machine.
CPU Types are either shared or dedicated. In a nutshell: shared CPU instances run lighter-weight tasks but potentially share CPU with other tenants. Shared VMs can have up to 2GB of memory. Dedicated CPU instances handle more demanding applications and can scale to 64GB of memory.
Upgrading a VM
You can easily change the type of your VMs. Just add the required size name to
fly scale vm and we’ll take care of the rest. For example to go from
fly scale vm dedicated-cpu-1x
Scaled VM size to dedicated-cpu-1x CPU Cores: 1 Memory: 2 GB
Adjusting a VM's Memory
fly scale memory command lets you directly set the VM memory allocation, in MB. For example, if we wanted our app to use 1GB of memory we'd run:
fly scale memory 1024
Scaled VM Memory size to 1 GB CPU Cores: 1 Memory: 1 GB
You can also change the VM type and memory size at the same time. The
fly scale vm command can take an additional memory flag which specifies the megabytes of RAM to be allocated to the VM. For example, if we wanted to allocate 4GB of RAM to our application and switch to a dedicated CPU option, we'd run:
fly scale vm dedicated-cpu-1x --memory 4096
Scaled VM size to dedicated-cpu-1x CPU Cores: 1 Memory: 4 GB
Viewing the Application's Scaled Status
To view where the instances of a Fly application are currently running, use
App Name = hellofly Owner = personal Version = 318 Status = running Hostname = hellofly.fly.dev Deployment Status ID = 8c3137c2-94d2-5fb6-e1ff-d46608def053 Version = v318 Status = running Description = Deployment is running Instances = 3 desired, 3 placed, 2 healthy, 0 unhealthy Instances ID VERSION REGION DESIRED STATUS HEALTH CHECKS RESTARTS CREATED a592ecf4 318 iad run running 1 total, 1 passing 0 1m7s ago 382dd4ce 318 lhr run running 1 total, 1 passing 0 1m33s ago 075c8c53 318 sjc run running 1 total, 1 passing 0 3m1s ago
Autoscaling is a horizontal scaling service based on a global pool of instances where the application can be run. The system will create at least the minimum number of application instances. The autoscaler will then create instances (scale-out) as total application load exceeds the
soft_limit * [instance count] threshold, up to the
max count. It will also remove instances (scale-in) when the max application load over a 10-minute window dips below the same threshold, down to the
min count. The 10-minute scale-in window allows for rapid scale-out with slightly more relaxed scale-in.
By default, autoscaling is
Disabled and manual count-based scaling is in operation.
To determine what the current autoscale settings of an application are, run
fly autoscale show:
fly autoscale show
Autoscaling: Enabled Min Count: 1 Max Count: 10
This app is configured with minimum of 1 instance and up to 10 instances that can be created on-demand.
Modifying the Autoscaling Plan
For example if you want to run at least three instances but no more than ten, you would run:
fly autoscale set min=3 max=10
Autoscaling: Enabled Min Count: 3 Max Count: 10
And if you wanted to change that to a minimum number of 5 instances, you would run:
fly autoscale set min=5
Autoscaling: Enabled Min Count: 5 Max Count: 10
You can continue to see your current scaling parameters using
fly scale show.
fly scale show
VM Resources for hellofly VM Size: shared-cpu-1x VM Memory: 256 MB Count: 5
The count field here now shows the number of instances currently running.
You can also turn off autoscaling and return to the recommended count-scaling option by disabling autoscaling:
fly autoscale disable