CODEWITHSUNDEEP
azure-api-management
Herb Stahl
Herb Stahl

Reputation: 439

Azure API Management Cache Issue

Goal: Use API Management cache-policy to cache a json response that never changes.

Original (no cache)
This policy is backed by an azure function that returns a never-changing json response. 

<policies>
    <inbound>
        <base />
        <set-backend-service id="apim-generated-policy" backend-id="azfunc-fluffyoauth2" />
        <rewrite-uri template="/WellKnownOpenidConfiguration" />
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>

Thinking that this might be a good thing to cache, I introduce the cache-lookup policy. 

<policies>
    <inbound>
        <base />
        <set-backend-service id="apim-generated-policy" backend-id="azfunc-fluffyoauth2" />
        <rewrite-uri template="/WellKnownOpenidConfiguration" />
        <cache-lookup vary-by-developer="false" vary-by-developer-groups="false" downstream-caching-type="none" />
    </inbound>
    <backend>
        <base />
    </backend>
    <outbound>
        <base />
        <cache-store duration="36000" />
    </outbound>
    <on-error>
        <base />
    </on-error>
</policies>

What I am seeing is that the cached version returns a binary that I believe is gzipped. This causes downstream code that expects it to be raw json to break. This reponse is an openid connect discovery document, and ironically if I point API Management's jwt-policy to this it breaks as well.

i.e. 

var auth0Domain = "https://apim-mycompany.azure-api.net/oauth2";
string responseString = null;
try
{
    var url = $"{auth0Domain}/.well-known/openid-configuration-cached";
    Console.WriteLine($"-------------------");
    Console.WriteLine($"{url}");
    var httpClient = new HttpClient();
    var response = await httpClient.GetAsync(new Uri($"{auth0Domain}/.well-known/openid-configuration-cached"));
    responseString = await response.Content.ReadAsStringAsync();
    Console.WriteLine($"-------------------");
    Console.WriteLine($"{responseString}");
    Console.WriteLine($"-------------------");
    JsonConvert.DeserializeObject<OpenIdConnectConfiguration>(responseString);
}
catch (Exception ex)
{
    Console.WriteLine($"Error:{ex.Message}");
    Console.WriteLine($"-------------------");
    return;
}



curl -I --location --request GET 'https://apim-fluffyoauth2.azure-api.net/oauth2/.well-known/openid-configuration-cached'
HTTP/1.1 200 OK
Cache-Control: no-store, must-revalidate, no-cache
Pragma: no-cache
Content-Length: 558
Content-Type: application/json; charset=utf-8
Content-Encoding: gzip
Expires: Tue, 14 Apr 2020 18:50:53 GMT
Vary: Accept-Encoding
Request-Context: appId=cid-v1:dfeba42c-e636-42bc-b501-7c77563c3e7b,appId=cid-v1:dfeba42c-e636-42bc-b501-7c77563c3e7b
Date: Tue, 14 Apr 2020 18:50:53 GMT

Question(s):

What is the cache-policy doing?
How can I change it to still cache but respond with what the NON-CACHED version does?

Upvotes: 0

Views: 2255

Answers (1)

Herb Stahl
Herb Stahl

Reputation: 439

Adding the following;

<cache-lookup vary-by-developer="false" vary-by-developer-groups="false" downstream-caching-type="none">
  <vary-by-header>Accept</vary-by-header>
  <vary-by-header>Accept-Charset</vary-by-header>
</cache-lookup>

Which produces the final policy. 

<policies>
<inbound>
    <base />
    <set-backend-service id="apim-generated-policy" backend-id="azfunc-fluffyoauth2" />
    <rewrite-uri template="/WellKnownOpenidConfiguration" />
    <cache-lookup vary-by-developer="false" vary-by-developer-groups="false" downstream-caching-type="none">
        <vary-by-header>Accept</vary-by-header>
        <vary-by-header>Accept-Charset</vary-by-header>
    </cache-lookup>
</inbound>
<backend>
    <base />
</backend>
<outbound>
    <base />
    <cache-store duration="3600" />
</outbound>
<on-error>
    <base />
</on-error>

Now results in API Management not doing a gzip encoding when it wasn't asked for.

I am still wondering why API Management will suddenly stop doing gzip encoding on the original problem. Sometimes it did it, then stop, which lead to some confusion as to what was going on.

Upvotes: 1

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