How to avoid HTTP 502/503 when accessing a REST API

[gaccardo-slb]

We are reading data from a REST API.  The process is fairly common: do one call to get a list of IDs, then do one or more calls for each ID to get the details.  For a small data set, everything works fine.  With a large number of IDs, the number of REST calls arriving at the server simulateously is extremely high.  This causes the server to return 502/503 errors and the data loading fails.

With other languages, a typical solution is to either make the calls sequentially instead of in parallel, or to rate-limit the calls in some way.  The reduces the onslaught of requests to the server and allows the server to answer the requests instead of rejecting them.  Is there a way to accomplish this with Power Query?

Regards,

G

[PhilipTreacy · Accepted solution]

Hi @gaccardo-slb 

You can use Function.InvokeAfter to introduce a delay between requests.  This code has a 2 second delay between web requests

let
    id_list = {1 .. 5},
    GetWeb = (id) => Json.Document(Web.Contents("https://jsonplaceholder.typicode.com/todos/" & Text.From(id))),
    Output = List.Transform(id_list, each Function.InvokeAfter( ()=>GetWeb(_), #duration(0,0,0,2)))    
in
    Output

regards

Phil

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[gaccardo-slb]

Beautiful!