apps/docs/content/troubleshooting/edge-function-503-response.mdx
A 503 HTTP status code from an Edge Function indicates one of three possible events:
SyntaxErrorThese require different fixes, so it is useful to decipher the cause before debugging:
If you received back a BOOT_ERROR message, like the one below, you can jump to the resolution section: Boot Error
{
"code": "BOOT_ERROR",
"message": "Function failed to start (please check logs)"
}
Otherwise, run the below query in your Log Explorer.
select
req.pathname as function_name,
res.status_code,
case
when metadata.execution_id is not null
and metadata.function_id is not null then 'app_level'
when metadata.execution_id is null
and metadata.function_id is not null then 'boot_error'
when metadata.execution_id is null
and metadata.function_id is null then 'internal_failure'
end as error_type
from
function_edge_logs
cross join UNNEST(metadata) as metadata
cross join UNNEST(metadata.request) as req
cross join UNNEST(metadata.response) as res
where status_code = 503
limit 50;
Depending on the output, you can use this table to find the appropriate debugging section:
| Value | Go to |
|---|---|
app_level | app level error |
boot_error | boot error - function cannot compile |
internal_failure | platform issue |
Somewhere in your function logic, you are returning a 503 response yourself:
return new Response(JSON.stringify(data), {
headers: { ...corsHeaders, 'Content-Type': 'application/json' },
status: 503, // <-- you set this
})
Check your function logic and any third-party API responses for where the 503 is originating.
503. Look for explicit status codes on Response objectsconsole.error('Returning 503 - reason:', reason)
See: Error handling in Edge Functions
A SyntaxError prevented your code from dynamically compiling.
In the Function Dashboard, under the affected function's Log tab, you can filter for the key phrase worker boot error:. the log will tell you syntax error occurred:
Alternatively, instead of using the Function Dashboard, you can programmatically find boot failure error messages in the Log Explorer with the below query:
select
fl.event_message,
content.timestamp,
fel.function_name,
fel.status_code
from
function_logs as fl
left join UNNEST(fl.metadata) as content on true
left join (
select
em.function_id,
em.version,
req.pathname as function_name,
res.status_code
from
function_edge_logs
left join UNNEST(metadata) as em on true
left join UNNEST(em.request) as req on true
left join UNNEST(em.response) as res on true
) as fel
on content.function_id = fel.function_id and content.version = fel.version
where content.event_type = 'BootFailure'
order by timestamp, function_name
limit 20;
Redefining a constant value can prevent the code from compiling:
let some_var
const some_var // SyntaxError — already declared
The log message for these errors should state the cause already declared and the file impacted.
worker boot error: Uncaught SyntaxError:
Identifier 'some_var' has already been declared at file:///var/tmp/sb-compile-edge-runtime/source/index.ts:6:7
Some key words can only be used in specific contexts. For instance, the await key word can only be used inside async functions.
(req: Request) => {
const { name } = await req.json(); // await only works inside async functions
}
The log message for these errors should state the cause Unexpected reserved word and the file impacted.
worker boot error: Uncaught SyntaxError:
Unexpected reserved word at file:///var/tmp/sb-compile-edge-runtime/source/index.ts:6:28
Imports can cause errors if they're not available within the edge function:
// importing non-existent module
import supabase from 'does_not_exist'
// or accessing non-existent export
import { doesNotExist } from 'jsr:@supabase/functions-js'
doesNotExist()
The log message for these errors should state the cause requested module... does not provide an export and the file impacted.
worker boot error: Uncaught SyntaxError:
The requested module 'jsr:@supabase/functions-js' does not provide an export named 'doesNotExist' at file:///var/tmp/sb-compile-edge-runtime/source/index.ts:2:10”
To fix, check the module and its imports to make sure they exist and are supported by Supabase Edge Functions.
If the module worked before, check to see if the most recent release had breaking changes and then only import the working version.
The edge function runtime is overwhelmed, or the API Gateway is returning its own 503 due to excessive load.
Open a support ticket and include the relevant log output from Step 1.