# Incident retro - 500'ing on the /images endpoint **Incident from:** 2021-11-15 **Incident until:** 2021-11-15 **Retro held:** 2021-11-17 * [Timeline](#timeline) * [Analysis of causes](#analysis-of-causes) * [Actions](#actions) ## Timeline 15 November 2021 See PR to add thumbnails to API 16:04 catalogue-api-gateway-5xx-alarm There were 4.0 errors in the API Alert repeated every 2-3 minutes until 16.57 16.06 AC We are reliably 500'ing on the /images endpoint: `,Attempt to decode value on failed cursor, List(DownField(type), DownField(thumbnail), DownField(data), DownField(canonicalWork), DownField(source)))` I suspect this is my change in internal model to make thumbnail a DigitalLocation – the API still expects that value to be a Location, so it’s looking for a type discriminator in type – but the ingestors are no longer setting that, because they see the type as unambiguous The fix is to roll the version of internal model in the API merged a change to add the license aggregation to the /images API 16.07 AFC I deployed the pipeline thinking it wasn’t a breaking change AC also didn’t think it was a breaking change 16.08 JG We’re still serving OK - assuming it’s because it’s only on some records? AFC I think it’s on everything that has a thumbnail, so quite a lot (edited) Couldn’t roll back because it’s on the pipeline side; have to roll the API forward 16.10 AC I would suggest: 1. Roll the internal model in the API 2. Deploy that I’m 98% sure that will fix it And I can explain the issue in a bit more detail in a bit 16.26 AC / AFC Some image queries would return a persistent error or queries that include those images in the results 16.31 AC We used to model `thumbnail: Location`, so it would be serialised as `{…, "type": "DigitalLocation"}` – this is how the API knows which flavour of Location it should deserialise Now we model `thumbnail: DigitalLocation` so it doesn’t get serialised by the ingestor with the `"type"` value. Then the API code doesn’t know how to interpret it. 16:31 It’s not fixed yet, but it will be shortly 16.49 AC Fix is rolling out now, alerts should be silencing shortly 16.57 catalogue-api-prod-5xx-alarm There were 2.0 errors in the API This was the final alert 17:04 NP No alerts for 5 mins ... all okay now? 17:25 AFC sorry natalie, it’s deployed so I think it’s fixed ## Analysis of causes The pipeline model had moved ahead of API: Change in internal model to make thumbnail a DigitalLocation – the API still expects that value to be a Location, so it’s looking for a type discriminator in type – but the ingestors are no longer setting that, because they see the type as unambiguous ## Actions No actions. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.wellcomecollection.org/incident-retros/2021-11-15_500ing-on-the-images-endpoint.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.