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5. Randomness

Available inall subroutines.

Identical to randomint, except takes an additional parameter used to seed the random number generator. This seed determines randomness. A consistent seed will provide a consistent result.

This function does not use secure random numbers and should not be used for cryptographic purposes.

Even though integer values in VCL are typically 64-bit signed integers, this VCL function only accepts from, to, and seed, which are signed 32-bit integers. The range of valid values for from, to, and seed is therefore −(2³¹) to 2³¹ − 1 inclusive. That is, the minimum and maximum values are -2147483648 and 2147483647 respectively, or -0x80000000 and 0x7FFFFFFF in hexadecimal.

This function is not prefixed with the std. namespace.

Example

if (randomint_seeded(0, 99, 555) < 5) {
  set req.http.X-ABTest = "A";
} else {
  set req.http.X-ABTest = "B";
}
if (randomint_seeded(-1, 0, 555) == -1) {
  set req.http.X-ABTest = "A";
} else {
  set req.http.X-ABTest = "B";
}

Try it out

randomint_seeded is used in the following code examples. Examples apply VCL to real-world use cases and can be deployed as they are, or adapted for your own service. See the full list of code examples for more inspiration.

Click RUN on a sample below to provision a Fastly service, execute the code on Fastly, and see how the function behaves.