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Scaling changes how much compute a process gets. You scale a process up by giving it a larger instance size, out by running more instances (by hand or with horizontal autoscaling), and the whole application down to zero with hibernation. Web processes and background workers scale; cron jobs and jobs run one instance per run and only take an instance size.

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Instance sizes

An instance size sets the CPU and memory of each instance of a process. Every instance of a process uses the same size. The dashboard shows sizes by name, in four groups: Hobby, Standard, CPU optimized and Memory optimized. Rules that come with the sizes:
  • H1 and custom domains. H1 is the only size in the Hobby group, and the dashboard also calls it the Hobby size. The web process can’t use H1 while the application has a custom domain, and you can’t add a custom domain while it uses H1.
  • Payment method. Without a payment method on the company, only H1 can be picked.
  • Limits are hard. A process that uses more memory than its size is stopped with exit code 137 and restarted. CPU use above the size is throttled, not stopped.
  • Local disk. Every instance also has up to 20 GB of ephemeral storage, whatever its size.
Each size’s price is shown next to it in the dashboard, per month for web processes and background workers and per minute for cron jobs and jobs. See Pricing.

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Change the size of a process

1

Open the process

In the sidebar, click Applications, then click the application. Click the Processes tab, click ⋯ on the process, then click Update process.
2

Pick the size

In Resource, pick the new size.
3

Save and deploy

Click Update process, then deploy the application. The process restarts on the new size.
Check the Analytics tab with Show limit on to see how close a process runs to its CPU and memory.

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Set the number of instances

Running more than one instance of the web process spreads requests across them and keeps the application up while one instance restarts. Every instance costs the same as the first.
1

Open the process

On the application’s Processes tab, click ⋯ on the web process or background worker, then click Update process.
2

Set the count

In Scaling, leave Horizontal auto-scaling off and drag Instance count to the number you want.
3

Save and deploy

Click Update process, then deploy the application.
A process with a disk is limited to 1 instance: adding a disk reduces a scaled process to one, and it can’t use autoscaling.

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Horizontal autoscaling

Horizontal autoscaling adds instances to a web process or background worker when its average CPU or memory use rises above a target, and removes them when use falls. The process never runs fewer than the minimum or more than the maximum instances you set. Sevalla scales up when either target is exceeded, and scales down when both are below their targets for the scale down interval. The Instance count chart on the Analytics tab shows how many instances ran and when. You pay for the instances that run, for as long as they run. Autoscaling isn’t available:
  • while hibernation is on, and you can’t turn hibernation on while any process autoscales;
  • for a process with a disk;
  • without a valid payment method on the company.

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Turn on autoscaling

1

Open the process

On the application’s Processes tab, click ⋯ on the web process or background worker, then click Update process.
2

Configure autoscaling

In Scaling, turn on Horizontal auto-scaling, set the minimum and maximum with the Instance count slider, and adjust the targets and steps if you need to.
3

Save and deploy

Click Update process, then deploy the application.
On the Processes tab, the process then reads Auto-scaling: 1 to 3 instances (with your values).

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Hibernation

Hibernation scales the application to zero when its domains receive no HTTP requests for the time you set, so its web process and background workers stop costing money while it’s idle. Use it for staging applications, demos and side projects. How hibernation works:
  • Going to sleep. After Hibernate after minutes without HTTP requests, Sevalla stops every instance of the web process. Background workers stop with it.
  • Waking up. The application wakes on the next HTTP request to any of its domains, usually within 90 seconds. Sevalla holds that first request for up to about 3 minutes while the application starts, then passes it on, or answers 503 if the application still isn’t ready. How long waking takes depends on how fast your application starts. Background workers start again with the web process.
  • Requests that aren’t held. Requests with a body larger than 50 MB, or without a Content-Length header, get a 503 while the application wakes instead of waiting.
  • Your own 503 responses. While hibernation is on, Sevalla retries any request your application answers with 503, for up to about 3 minutes, before it passes the 503 on.
  • What doesn’t wake it. Only HTTP requests to the application’s domains wake it. Connections through a TCP proxy or from other services on the private network don’t.
  • What keeps running. Cron jobs and jobs run on their own schedule, whether the application sleeps or not.
Hibernation needs HTTP traffic on: it has no effect while the web process’s HTTP traffic is off. It also can’t be on while any process uses horizontal autoscaling.
Anything held in memory or on an instance’s ephemeral filesystem is lost when the application goes to sleep. Keep sessions and queues in a database or on a disk.

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Turn on hibernation

1

Open the hibernation settings

In the sidebar, click Applications, then click the application. Click the Settings tab, then click Update hibernation in the Hibernation section.
2

Set the idle time

Turn on Hibernation and enter Hibernate after: the minutes without HTTP requests before the application scales to zero, from 1 to 10000. The default is 5.
3

Save

Click Update hibernation. The change applies to the running application, without a deployment.
The Update hibernation sheet with the Hibernation switch on and Hibernate after set to 5 minutesThe Update hibernation sheet with the Hibernation switch on and Hibernate after set to 5 minutes
The Hibernation section of the Settings tab then reads Hibernate after with your value, in minutes of inactivity. To turn it off, open the same sheet, turn off Hibernation and click Update hibernation.

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What scaling costs

You pay for each instance of each process, by its size, for the time it runs: Disks, bandwidth and build time are billed separately. See Pricing and How billing works.

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API and CLI