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apim-policy.xml
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apim-policy.xml
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<policies>
<inbound>
<base />
<!-- Getting the main variable where we keep the list of backends -->
<cache-lookup-value key="listBackends" variable-name="listBackends" />
<!-- If we can't find the variable, initialize it -->
<choose>
<when condition="@(context.Variables.ContainsKey("listBackends") == false)">
<set-variable name="listBackends" value="@{
// -------------------------------------------------
// ------- Explanation of backend properties -------
// -------------------------------------------------
// "url": Your backend url
// "priority": Lower value means higher priority over other backends.
// If you have more one or more Priority 1 backends, they will always be used instead
// of Priority 2 or higher. Higher values backends will only be used if your lower values (top priority) are all throttling.
// "isThrottling": Indicates if this endpoint is returning 429 (Too many requests) currently
// "retryAfter": We use it to know when to mark this endpoint as healthy again after we received a 429 response
JArray backends = new JArray();
backends.Add(new JObject()
{
{ "url", "https://andre-openai-eastus.openai.azure.com/" },
{ "priority", 1},
{ "isThrottling", false },
{ "retryAfter", DateTime.MinValue }
});
backends.Add(new JObject()
{
{ "url", "https://andre-openai-eastus-2.openai.azure.com/" },
{ "priority", 1},
{ "isThrottling", false },
{ "retryAfter", DateTime.MinValue }
});
backends.Add(new JObject()
{
{ "url", "https://andre-openai-northcentralus.openai.azure.com/" },
{ "priority", 1},
{ "isThrottling", false },
{ "retryAfter", DateTime.MinValue }
});
backends.Add(new JObject()
{
{ "url", "https://andre-openai-canadaeast.openai.azure.com/" },
{ "priority", 2},
{ "isThrottling", false },
{ "retryAfter", DateTime.MinValue }
});
backends.Add(new JObject()
{
{ "url", "https://andre-openai-francecentral.openai.azure.com/" },
{ "priority", 3},
{ "isThrottling", false },
{ "retryAfter", DateTime.MinValue }
});
backends.Add(new JObject()
{
{ "url", "https://andre-openai-uksouth.openai.azure.com/" },
{ "priority", 3},
{ "isThrottling", false },
{ "retryAfter", DateTime.MinValue }
});
backends.Add(new JObject()
{
{ "url", "https://andre-openai-westeurope.openai.azure.com/" },
{ "priority", 3},
{ "isThrottling", false },
{ "retryAfter", DateTime.MinValue }
});
backends.Add(new JObject()
{
{ "url", "https://andre-openai-australia.openai.azure.com/" },
{ "priority", 4},
{ "isThrottling", false },
{ "retryAfter", DateTime.MinValue }
});
return backends;
}" />
<!-- And store the variable into cache again -->
<cache-store-value key="listBackends" value="@((JArray)context.Variables["listBackends"])" duration="60" />
</when>
</choose>
<authentication-managed-identity resource="https://cognitiveservices.azure.com" output-token-variable-name="msi-access-token" ignore-error="false" />
<set-header name="Authorization" exists-action="override">
<value>@("Bearer " + (string)context.Variables["msi-access-token"])</value>
</set-header>
<set-variable name="backendIndex" value="-1" />
<set-variable name="remainingBackends" value="1" />
</inbound>
<backend>
<retry condition="@(context.Response != null && (context.Response.StatusCode == 429 || context.Response.StatusCode >= 500) && ((Int32)context.Variables["remainingBackends"]) > 0)" count="50" interval="0">
<!-- Before picking the backend, let's verify if there is any that should be set to not throttling anymore -->
<set-variable name="listBackends" value="@{
JArray backends = (JArray)context.Variables["listBackends"];
for (int i = 0; i < backends.Count; i++)
{
JObject backend = (JObject)backends[i];
if (backend.Value<bool>("isThrottling") && DateTime.Now >= backend.Value<DateTime>("retryAfter"))
{
backend["isThrottling"] = false;
backend["retryAfter"] = DateTime.MinValue;
}
}
return backends;
}" />
<cache-store-value key="listBackends" value="@((JArray)context.Variables["listBackends"])" duration="60" />
<!-- This is the main logic to pick the backend to be used -->
<set-variable name="backendIndex" value="@{
JArray backends = (JArray)context.Variables["listBackends"];
int selectedPriority = Int32.MaxValue;
List<int> availableBackends = new List<int>();
for (int i = 0; i < backends.Count; i++)
{
JObject backend = (JObject)backends[i];
if (!backend.Value<bool>("isThrottling"))
{
int backendPriority = backend.Value<int>("priority");
if (backendPriority < selectedPriority)
{
selectedPriority = backendPriority;
availableBackends.Clear();
availableBackends.Add(i);
}
else if (backendPriority == selectedPriority)
{
availableBackends.Add(i);
}
}
}
if (availableBackends.Count == 1)
{
return availableBackends[0];
}
if (availableBackends.Count > 0)
{
//Returns a random backend from the list if we have more than one available with the same priority
return availableBackends[new Random().Next(0, availableBackends.Count)];
}
else
{
//If there are no available backends, the request will be sent to the first one
return 0;
}
}" />
<set-variable name="backendUrl" value="@(((JObject)((JArray)context.Variables["listBackends"])[(Int32)context.Variables["backendIndex"]]).Value<string>("url") + "/openai")" />
<set-backend-service base-url="@((string)context.Variables["backendUrl"])" />
<forward-request buffer-request-body="true" />
<choose>
<!-- In case we got 429 or 5xx from a backend, update the list with its status -->
<when condition="@(context.Response != null && (context.Response.StatusCode == 429 || context.Response.StatusCode >= 500) )">
<cache-lookup-value key="listBackends" variable-name="listBackends" />
<set-variable name="listBackends" value="@{
JArray backends = (JArray)context.Variables["listBackends"];
int currentBackendIndex = context.Variables.GetValueOrDefault<int>("backendIndex");
int retryAfter = Convert.ToInt32(context.Response.Headers.GetValueOrDefault("Retry-After", "-1"));
if (retryAfter == -1)
{
retryAfter = Convert.ToInt32(context.Response.Headers.GetValueOrDefault("x-ratelimit-reset-requests", "-1"));
}
if (retryAfter == -1)
{
retryAfter = Convert.ToInt32(context.Response.Headers.GetValueOrDefault("x-ratelimit-reset-tokens", "10"));
}
JObject backend = (JObject)backends[currentBackendIndex];
backend["isThrottling"] = true;
backend["retryAfter"] = DateTime.Now.AddSeconds(retryAfter);
return backends;
}" />
<cache-store-value key="listBackends" value="@((JArray)context.Variables["listBackends"])" duration="60" />
<set-variable name="remainingBackends" value="@{
JArray backends = (JArray)context.Variables["listBackends"];
int remainingBackends = 0;
for (int i = 0; i < backends.Count; i++)
{
JObject backend = (JObject)backends[i];
if (!backend.Value<bool>("isThrottling"))
{
remainingBackends++;
}
}
return remainingBackends;
}" />
</when>
</choose>
</retry>
</backend>
<outbound>
<base />
<!-- This will return the used backend URL in the HTTP header response. Remove it if you don't want to expose this data -->
<set-header name="x-openai-backendurl" exists-action="override">
<value>@(context.Variables.GetValueOrDefault<string>("backendUrl", "none"))</value>
</set-header>
</outbound>
<on-error>
<base />
</on-error>
</policies>