---
header: Compute resource limits
lang: en
last_updated: '2026-02-17'
url: https://docs.fastly.com/products/compute-resource-limits
---

This guide details Fastly resource limits for [Compute](https://docs.fastly.com/products/compute) services. These limits change based on whether you're using a free account or have purchased one of our [packaged offerings](https://www.fastly.com/package-entitlements/). These limits may be further defined on your service order.

> **NOTE:** In addition to the limits described here, Compute services can also be limited by the products or platform services that you access through your application code. Check out our [network services resource limits](https://docs.fastly.com/products/network-services-resource-limits) for additional details.

## Port limits

Compute services accept client connections on port 443 only. This is different from VCL services, which support client connections on port 80.

> **NOTE:** If your Compute service receives a request on port 80, Fastly automatically returns a 308 Permanent Redirect response status with the `Location` header indicating the HTTPS version of the same URL in a `Location` header.

## Default limits

Item | Limit | Scope
-----|-------|------
Maximum compiled package size | 100MB | per service
Maximum cached object size | 100MB | per object
Maximum CPU time available to a single request instance | 50ms | per execution
Maximum runtime for a single request instance | 2 min (60s for trial accounts) | per execution
Maximum memory consumption | 1M bytes stack, 128MB heap | per execution
Maximum number of dictionary lookups | 32 | per execution
Maximum number of backend requests | 32 (10 for trial accounts) | per execution
Maximum number of dynamic backends | 200 | per service
[Vary rules](https://www.fastly.com/documentation/guides/concepts/edge-state/cache/#limitations-and-constraints) | 8 | per cache object
Maximum length of a request header | 128KB | per header
Maximum length of a response header | 128KB | per header
Maximum length of a method name | 8192 bytes | per request
Maximum length of a URL | 8192 bytes | per request

An *execution* refers to a single instance of a Compute program being executed, normally in response to a client HTTP request. Separate limits also apply to the use of [log tailing](https://www.fastly.com/documentation/guides/integrations/streaming-logs/setting-up-remote-log-streaming-for-compute) with Compute services.

## Service chain limits

Item | Limit | Implications
-----|-------|-------------
Service chains and hops | 20 hops, 6 unique services | Read our [developer information about loop detection](https://www.fastly.com/documentation/guides/concepts/service-chaining/#loop-detection) for more info.

## Edge data storage limitations

Limits for each of our [edge data storage](https://docs.fastly.com/products/edge-data-storage) options differ if you've purchased a [package offering](https://www.fastly.com/package-entitlements/) or are using a [product or feature trial](https://www.fastly.com/documentation/guides/account-info/billing/account-types).

The default limit for the number of shared resources (Config Store, KV Store, Secret Store, and ACLs on Compute combined) is 100. To raise this limit, contact your account manager.

### Edge data storage naming restrictions

When naming a store, whether through the [web interface](https://www.fastly.com/documentation/guides/compute/edge-data-storage/) or [API](https://www.fastly.com/documentation/reference/api/services/resources/), be aware of the following restrictions:

- Store names must be unique.
- Store names must begin with an ASCII alphabetical character and contain only ASCII alphanumeric and underscore characters.
- Store names cannot be an empty string.

### Config Store

Config Store is included with your Compute service with the following limitations.

Item | Trial limit | Paid account limit | Implications
-----|-------------|--------------------|-------------
Config stores | 1 | 5 | Paid accounts can purchase additional stores for a monthly fee.
Config store entries (per store) | 100 | 500 | An error informs you that you've exceeded the limit.
Config store key length | 255 characters | 255 characters | An error informs you that you've exceeded the limit.
Config store value length | 8,000 characters | 8,000 characters | An error informs you that you've exceeded the limit.
Config store write operations | 1000 writes per hour | 1000 writes per hour | Write limits are shared with all other Fastly API calls. Exceeding the limit will result in an API limit error. Refer to [API rate limiting](https://www.fastly.com/documentation/reference/api/#rate-limiting) for more info.

### KV Store

KV Store is an add-on and is priced in addition to Compute services. The number of KV Stores is limited to the account’s available resources allotment. The following limitations also apply:

- Values stored in KV Store items are limited by default to 25MB, but that limit can be raised to as much as 100MB upon request. Contact your account manager or [sales@fastly.com](mailto:sales@fastly.com) for more information.
- Metadata stored in KV Store items is limited to 2000 bytes and must be composed of Unicode characters encoded using UTF-8.
- KV Stores have a rate limit of 1,000 writes per second per store, and 5,000 reads per second per store. These are soft limits for the durable store and they auto-scale as needed.
- KV Store items have a rate limit of 1 write per second per item.
- KV Store item batch requests have a limit of 100,000 items per request.
- KV Stores provide [eventual consistency](https://en.wikipedia.org/wiki/Eventual_consistency), which means that reading a key immediately after writing it may not return the updated value.

#### Key limitations

- Keys cannot start with `.well-known/acme-challenge/`, `.`, or `..`.
- Key names can contain any sequence of valid Unicode characters of length 1-1024 bytes when UTF-8 encoded. The following characters can be used in key names but can't be searched in a prefix query string: `!`, `"`, `$`, `%`, `&`, `(`, `)`, `*`, `+`, `,`, `/`, `\`, `:`, `<`, `=`, `>`, `@`, `[`, `]`, `` ` ``, `{`, `}`.
- Keys cannot use [Unicode characters](https://www.w3schools.com/charsets/ref_html_utf8.asp) 0 through 32, 65534, and 65535 as single-character key names.
- The following characters cannot be used in key names:
  - `#`, `;`, `?`, `^`, and `|`
  - line feed (LF) characters
  - carriage-return (CR) characters