anomalyco/sst · error · VisibleError

Durable functions require "logging.format" to be set to "jso

Error message

Durable functions require "logging.format" to be set to "json"

What it means

Durable functions persist structured state and therefore require JSON-formatted logs. If you explicitly set logging.format to anything other than "json" on a function created with `durable: true`, normalizeLogging() throws this error.

Source

Thrown at platform/src/components/aws/function.ts:1949

      });
    }

    function normalizeStreaming() {
      return output(args.streaming).apply((streaming) => streaming ?? false);
    }

    function normalizeLogging() {
      return output(args.logging).apply((logging) => {
        if (logging === false) return undefined;

        if (logging?.retention && logging?.logGroup) {
          throw new VisibleError(
            `Cannot set both "logging.retention" and "logging.logGroup"`,
          );
        }

        if (args.durable && logging?.format && logging?.format != "json") {
          throw new VisibleError(
            `Durable functions require "logging.format" to be set to "json"`,
          );
        }

        const defaultFormat = args.durable ? "json" : "text";

        return {
          logGroup: logging?.logGroup,
          retention: logging?.retention ?? "1 month",
          format: logging?.format ?? defaultFormat,
        };
      });
    }

    function normalizeVolume() {
      if (!args.volume) return;

      return output(args.volume).apply((volume) => ({

View on GitHub (pinned to a0bd20f762)

Solutions

1. Set logging: { format: "json" } on the durable function
2. Remove the explicit format so the durable default of "json" applies
3. Move `durable: false` if you genuinely need text logs

Example fix

// before
new sst.aws.Function("Fn", { durable: true, logging: { format: "text" } });
// after
new sst.aws.Function("Fn", { durable: true, logging: { format: "json" } });

if (args.durable && args.logging && typeof args.logging === "object" && args.logging.format && args.logging.format !== "json")
  throw new Error("Durable functions need logging.format = 'json'");

try {
  new sst.aws.Function("Fn", { durable: true, logging });
} catch (e) {
  if ((e as Error).message.includes("Durable functions require")) {
    console.error("Set logging.format to json or omit it");
  }
  throw e;
}

When it happens

Trigger: Creating a Function with `durable: true` and `logging: { format: "text" }` (or any non-json format).

Common situations: Copy-pasting a standard function's logging config into a durable function; team-wide logging defaults forcing format: "text".

Related errors

• Cannot set both "logging.retention" and "logging.logGroup"
• You must provide a KMS key via `kmsKey` when configuring `cu
• Copy destination path "${to}" must be relative
• The "vpc.subnets" property has been renamed to "vpc.privateS
• result.errors.join("\n")

AI-assisted analysis of anomalyco/sst@a0bd20f762 (2026-08-30). Data as JSON: /api/errors/9071138d8c3b95d5. Report an issue: GitHub.