How do I construct this url rewrite policy in Azure APIM? - azure

Question

In Azure APIM, looking for a url rewrite policy (I think), that looks for a certain string and constructs the backend url based on that string.
Example1:
Converts this
https://myfrontend.com/locations/usa/remaining-url
to this
https://usa.com/remaining-url
Example1:
Converts this
https://myfrontend.com/locations/canada/remaining-url
to this
https://canada.com/remaining-url

Answer 1

It depends on your API Management API / Operation.
In my example I designed it this way:
'/locations/{locationid}/*':
get:
summary: Locations with Id
operationId: locations-with-id
parameters:
- name: locationid
in: path
required: true
schema:
enum:
- usa
- canada
type: string
There's a matchedparameter locationid which will be used in the policy.
The path ends with a wildcard /* to support the remaining URL.
For getting the remaining URL, the following Regex is used:
\/locations\/[^\/]*(\/[a-zA-Z0-9-?=#_]*)
API with operation GET /locations/{locationid}/* :
Operation policy:
<policies>
<inbound>
<base />
<set-variable name="RegexLocation" value="\/locations\/[^\/]*(\/[a-zA-Z0-9-?=#_]*)" />
<set-variable name="remainingUrl" value="#{
string pattern = context.Variables.GetValueOrDefault<string>("RegexLocation");
var regex = new Regex(pattern);
var match = regex.Match(context.Request.OriginalUrl.Path.ToString());
if (match.Success)
{
return match.Groups[1].Value;;
}
else
{
return string.Empty;
}
}" />
<choose>
<when condition="#(context.Request.MatchedParameters.GetValueOrDefault("locationid", "") == "usa")">
<set-backend-service base-url="https://usa.com" />
</when>
<when condition="#(context.Request.MatchedParameters.GetValueOrDefault("locationid", "") == "canada")">
<set-backend-service base-url="https://canada.com" />
</when>
</choose>
<rewrite-uri template="#(context.Variables.GetValueOrDefault<string>("remainingUrl"))" copy-unmatched-params="true" />
</inbound>
<backend>
<base />
</backend>
<outbound>
<base />
</outbound>
<on-error>
<base />
</on-error>
</policies>
The choose policy is used to specify the backend.
The policy rewrite-uri adds the renaming path and query
Output from trace for request:
GET https://rfqapiservicey27itmeb4cf7q.azure-api.net/abc/locations/usa/lorem?ipsum=1
The new backend URL is:
https://usa.com/lorem?ipsum=1
{
"traceEntries": {
"inbound": [
{
"source": "set-variable",
"timestamp": "2022-08-13T07:08:45.5496188Z",
"elapsed": "00:00:00.0003989",
"data": {
"message": "Context variable was successfully set.",
"name": "RegexLocation",
"value": "\\/locations\\/[^\\/]*(\\/[a-zA-Z0-9-?=#_]*)"
}
},
{
"source": "set-variable",
"timestamp": "2022-08-13T07:08:45.5496188Z",
"elapsed": "00:00:00.0004445",
"data": {
"message": "Expression was successfully evaluated.",
"expression": "\n string pattern = context.Variables.GetValueOrDefault<string>(\"RegexLocation\");\n\n var regex = new Regex(pattern);\n var match = regex.Match(context.Request.OriginalUrl.Path.ToString());\n\n if (match.Success)\n { \n return match.Groups[1].Value;;\n } \n else\n {\n return string.Empty;\n }\n\n ",
"value": "/lorem"
}
},
{
"source": "set-variable",
"timestamp": "2022-08-13T07:08:45.5496188Z",
"elapsed": "00:00:00.0004465",
"data": {
"message": "Context variable was successfully set.",
"name": "remainingUrl",
"value": "/lorem"
}
},
{
"source": "choose",
"timestamp": "2022-08-13T07:08:45.5496188Z",
"elapsed": "00:00:00.0004581",
"data": {
"message": "Expression was successfully evaluated.",
"expression": "context.Request.MatchedParameters.GetValueOrDefault(\"locationid\", \"\") == \"usa\"",
"value": true
}
},
{
"source": "set-backend-service",
"timestamp": "2022-08-13T07:08:45.5496188Z",
"elapsed": "00:00:00.0004690",
"data": {
"message": "Backend service URL was changed.",
"oldBackendServiceUrl": "https://rfqapiservicey27itmeb4cf7q.azure-api.net/abc",
"newBackendServiceUrl": "https://usa.com/",
"request": { "url": "https://usa.com/locations/usa/lorem?ipsum=1" }
}
},
{
"source": "rewrite-uri",
"timestamp": "2022-08-13T07:08:45.5496188Z",
"elapsed": "00:00:00.0004757",
"data": {
"message": "Expression was successfully evaluated.",
"expression": "context.Variables.GetValueOrDefault<string>(\"remainingUrl\")",
"value": "/lorem"
}
},
{
"source": "rewrite-uri",
"timestamp": "2022-08-13T07:08:45.5496188Z",
"elapsed": "00:00:00.0005407",
"data": {
"message": "Updated request URL per specified rewrite template.",
"request": { "url": "https://usa.com/lorem?ipsum=1" }
}
}
],
"backend": [
{
"source": "forward-request",
"timestamp": "2022-08-13T07:08:45.5496188Z",
"elapsed": "00:00:00.0007386",
"data": {
"message": "Request is being forwarded to the backend service. Timeout set to 300 seconds",
"request": {
"method": "GET",
"url": "https://usa.com/lorem?ipsum=1"
}
}
}
]
}
}