Backend plugin middleware does not execute response modifier if proxy returns an error in at least 1 backend #597
Comments
This was referenced Aug 9, 2022
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We didn't review this yet, but I am curious to know why you closed the PR. |
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@alombarte sorry for the late reply, nothing to do with the code, I agree that it is a bug that needs fixing. |
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Any updates regarding this bug? |
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Environment info:
Describe the bug
plugin/req-resp-modifier in an endpoint is not called if one of the backend CEL evaluations fails
this was initially submitted in krakend/krakend-ce#542
After some debugging it looks like it's an issue in the plugin.go in the proxy pkg https://github.com/luraproject/lura/blob/master/proxy/plugin.go#L91-L96
When receiving a merged response for multiple backends, if one of the backends fails, we get a non nil err that is a mergeError.
The error contains a slice with one entry per failed backend.
Tested a simple fix, check if resp is nil, this still returns error and does not call the response modifier when all backends fail or is just one that failed, while allowing for the modifier to still be called.
Your configuration file:
{ "$schema": "https://www.krakend.io/schema/v3.json", "version": 3, "name": "conditional test", "timeout": "3000s", "cache_ttl": "300s", "output_encoding": "json", "disable_rest": false, "plugin": { "folder": "./plugins/", "pattern": ".so" }, "extra_config": { "telemetry/logging": { "level": "DEBUG", "prefix": "[KRAKEND]", "syslog": false, "stdout": true } }, "endpoints": [ { "endpoint": "/services", "input_headers": [ "X-Group-Id" ], "method": "GET", "output_encoding": "json-collection", "extra_config": { "plugin/req-resp-modifier": { "name": [ "krakend-response-aggregator" ] } }, "backend": [ { "group": "app1", "url_pattern": "/pattern1", "encoding": "safejson", "sd": "static", "method": "GET", "host": [ "localhost:8090" ], "extra_config": { "validation/cel": [ { "check_expr": "'group1' in req_headers['X-Group-Id']" } ] } }, { "group": "app2", "url_pattern": "/pattern1", "encoding": "safejson", "sd": "static", "method": "GET", "host": [ "localhost:8090" ], "extra_config": { "validation/cel": [ { "check_expr": "'group2' in req_headers['X-Group-Id']" } ] } }, { "group": "app3", "url_pattern": "/pattern2", "encoding": "safejson", "sd": "static", "method": "GET", "host": [ "localhost:8090" ], "extra_config": { "validation/cel": [ { "check_expr": "'group1' in req_headers['X-Group-Id']" } ] } } ] } ] }Configuration check output:
Result of
krakend check -dtc krakend_conditional.json --lintcommandCommands used:
How did you start the software?
Expected behavior
The objective is to call multiple backends on a endpoint conditionally and return each backend response as a JSON collection where each element is the backend response.
Each backend is called if an HTTP header values matches a condition.
Each backend has a group defined and I have written a response modifier plugin that applied to the endpoint gets the merged response and then collapses each group response and moves the group key name to the value of
"name"into the each backend response and adds the response collection to a"collection"object.So each backend returns something in the likes of
{ "groupId": "group1", "url": "/pattern1" }Merged response would look like
{ "app1": { "groupId": "group1", "url": "/pattern1" }, "app3": { "groupId": "group1", "url": "/pattern2" } }And modified response by the custom plugin:
{ "collection": [ { "name": "app1", "groupId": "group1", "url": "/pattern1" }, { "name": "app3", "groupId": "group1", "url": "/pattern2" } ] }With
output_encodingasjson-collectionwe would get:[ { "name": "app1", "groupId": "group1", "url": "/pattern1" }, { "name": "app3", "groupId": "group1", "url": "/pattern2" } ]Call to
servicesendpoint should return the expected collection resulting of the custom plugin response modification but instead returns an empty JSON collectionSetting the endpoint's
output_encodingtojsonshows that the backend responses were merged but the response modifier was not triggered.{ "app1": { "groupId": "group1", "url": "/pattern1" }, "app3": { "groupId": "group1", "url": "/pattern2" } }Logs:
The custom-plugin has logging and it should be visible with debug
Additional comments:
Changing the CEL expression with group2 to group1 so that all backends pass the CEL evaluation proves that the custom plugin works when called
Logs
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