Monitoring metrics and logs in Azure Front Door

By using Azure Front Door, you can monitor resources in the following ways:

  • Metrics. Azure Front Door currently has eight metrics to view performance counters.
  • Logs. Activity and diagnostic logs allow performance, access, and other data to be saved or consumed from a resource for monitoring purposes.

Metrics

Metrics are a feature for certain Azure resources that allow you to view performance counters in the portal. The following are available Front Door metrics:

Metric Metric Display Name Unit Dimensions Description
RequestCount Request Count Count HttpStatus
HttpStatusGroup
ClientRegion
ClientCountry
The number of client requests served by Front Door.
RequestSize Request Size Bytes HttpStatus
HttpStatusGroup
ClientRegion
ClientCountry
The number of bytes sent as requests from clients to Front Door.
ResponseSize Response Size Bytes HttpStatus
HttpStatusGroup
ClientRegion
ClientCountry
The number of bytes sent as responses from Front Door to clients.
TotalLatency Total Latency Milliseconds HttpStatus
HttpStatusGroup
ClientRegion
ClientCountry
The total time from the client request received by Front Door until the last response byte sent from AFD to client.
BackendRequestCount Backend Request Count Count HttpStatus
HttpStatusGroup
Backend
The number of requests sent from Front Door to backends.
BackendRequestLatency Backend Request Latency Milliseconds Backend The time calculated from when the request was sent by Front Door to the backend until Front Door received the last response byte from the backend.
BackendHealthPercentage Backend Health Percentage Percent Backend
BackendPool
The percentage of successful health probes from Front Door to backends.
WebApplicationFirewallRequestCount Web Application Firewall Request Count Count PolicyName
RuleName
Action
The number of client requests processed by the application layer security of Front Door.

Activity logs

Activity logs provide information about the operations done on Front Door. They also determine the what, who, and when for any write operations (put, post, or delete) taken on Front Door.

Note

Activity logs don't include read (get) operations. They also don't include operations that you perform by using either the Azure portal or the original Management API.

Access activity logs in your Front Door or all the logs of your Azure resources in Azure Monitor. To view activity logs:

  1. Select your Front Door instance.

  2. Select Activity log.

    Activity log

  3. Choose a filtering scope, and then select Apply.

Diagnostic logs

Diagnostic logs provide rich information about operations and errors that are important for auditing and troubleshooting. Diagnostic logs differ from activity logs.

Activity logs provide insights into the operations done on Azure resources. Diagnostic logs provide insight into operations that your resource has done. For more information, see Azure Monitor diagnostic logs.

Diagnostic logs

To configure diagnostic logs for your Front Door:

  1. Select your Azure Front Door.

  2. Choose Diagnostic settings.

  3. Select Turn on diagnostics. Archive diagnostic logs along with metrics to a storage account, stream them to an event hub, or send them to Azure Monitor logs.

Front Door currently provides diagnostic logs. Diagnostic logs provide individual API requests with each entry having the following schema:

Property Description
BackendHostname If request was being forwarded to a backend, this field represents the hostname of the backend. This field will be blank if the request gets redirected or forwarded to a regional cache (when caching gets enabled for the routing rule).
CacheStatus For caching scenarios, this field defines the cache hit/miss at the POP
ClientIp The IP address of the client that made the request. If there was an X-Forwarded-For header in the request, then the Client IP is picked from the same.
ClientPort The IP port of the client that made the request.
HttpMethod HTTP method used by the request.
HttpStatusCode The HTTP status code returned from the proxy.
HttpStatusDetails Resulting status on the request. Meaning of this string value can be found at a Status reference table.
HttpVersion Type of the request or connection.
POP Short name of the edge where the request landed.
RequestBytes The size of the HTTP request message in bytes, including the request headers and the request body.
RequestUri URI of the received request.
ResponseBytes Bytes sent by the backend server as the response.
RoutingRuleName The name of the routing rule that the request matched.
RulesEngineMatchNames The names of the rules that the request matched.
SecurityProtocol The TLS/SSL protocol version used by the request or null if no encryption.
SentToOriginShield
(deprecated) * See notes on deprecation in the following section.
If true, it means that request was answered from origin shield cache instead of the edge pop. Origin shield is a parent cache used to improve cache hit ratio.
isReceivedFromClient If true, it means that the request came from the client. If false, the request is a miss in the edge (child POP) and is responded from origin shield (parent POP).
TimeTaken The length of time from first byte of request into Front Door to last byte of response out, in seconds.
TrackingReference The unique reference string that identifies a request served by Front Door, also sent as X-Azure-Ref header to the client. Required for searching details in the access logs for a specific request.
UserAgent The browser type that the client used.
ErrorInfo This field contains the specific type of error for further troubleshooting.
Possible values include:
NoError: Indicates no error was found.
CertificateError: Generic SSL certificate error.
CertificateNameCheckFailed: The host name in the SSL certificate is invalid or doesn't match.
ClientDisconnected: Request failure because of client network connection.
UnspecifiedClientError: Generic client error.
InvalidRequest: Invalid request. It might occur because of malformed header, body, and URL.
DNSFailure: DNS Failure.
DNSNameNotResolved: The server name or address couldn't be resolved.
OriginConnectionAborted: The connection with the origin was stopped abruptly.
OriginConnectionError: Generic origin connection error.
OriginConnectionRefused: The connection with the origin wasn't able to established.
OriginError: Generic origin error.
OriginInvalidResponse: Origin returned an invalid or unrecognized response.
OriginTimeout: The timeout period for origin request expired.
ResponseHeaderTooBig: The origin returned too large of a response header.
RestrictedIP: The request was blocked because of restricted IP.
SSLHandshakeError: Unable to establish connection with origin because of SSL hand shake failure.
UnspecifiedError: An error occurred that didn’t fit in any of the errors in the table.

Sent to origin shield deprecation

The raw log property isSentToOriginShield has been deprecated and replaced by a new field isReceivedFromClient. Use the new field if you're already using the deprecated field.

Raw logs include logs generated from both CDN edge (child POP) and origin shield. Origin shield refers to parent nodes that are strategically located across the globe. These nodes communicate with origin servers and reduce the traffic load on origin.

For every request that goes to origin shield, there are 2-log entries:

  • One for edge nodes
  • One for origin shield.

To differentiate the egress or responses from the edge nodes vs. origin shield, you can use the field isReceivedFromClient to get the correct data.

If the value is false, then it means the request is responded from origin shield to edge nodes. This approach is effective to compare raw logs with billing data. Charges aren't incurred for egress from origin shield to the edge nodes. Charges are incurred for egress from the edge nodes to clients.

Kusto query sample to exclude logs generated on origin shield in Log Analytics.

AzureDiagnostics | where Category == "FrontdoorAccessLog" and isReceivedFromClient_b == true

Note

For various routing configurations and traffic behaviors, some of the fields like backendHostname, cacheStatus, isReceivedFromClient, and POP field may respond with different values. The below table explains the different values these fields will have for various scenarios:

Scenarios Count of log entries POP BackendHostname isReceivedFromClient CacheStatus
Routing rule without caching enabled 1 Edge POP code Backend where request was forwarded True CONFIG_NOCACHE
Routing rule with caching enabled. Cache hit at the edge POP 1 Edge POP code Empty True HIT
Routing rule with caching enabled. Cache misses at edge POP but cache hit at parent cache POP 2 1. Edge POP code
2. Parent cache POP code
1. Parent cache POP hostname
2. Empty
1. True
2. False
1. MISS
2. HIT
Routing rule with caching enabled. Caches miss at edge POP but PARTIAL cache hit at parent cache POP 2 1. Edge POP code
2. Parent cache POP code
1. Parent cache POP hostname
2. Backend that helps populate cache
1. True
2. False
1. MISS
2. PARTIAL_HIT
Routing rule with caching enabled. Cache PARTIAL_HIT at edge POP but cache hit at parent cache POP 2 1. Edge POP code
2. Parent cache POP code
1. Edge POP code
2. Parent cache POP code
1. True
2. False
1. PARTIAL_HIT
2. HIT
Routing rule with caching enabled. Cache misses at both edge and parent cache POPP 2 1. Edge POP code
2. Parent cache POP code
1. Edge POP code
2. Parent cache POP code
1. True
2. False
1. MISS
2. MISS

Note

For caching scenarios, the value for Cache Status will be partial_hit when some of the bytes for a request get served from Front Door edge or origin shield cache while some of the bytes get served from the origin for large objects.

Front Door uses a technique called object chunking. When a large file is requested, the Front Door retrieves smaller pieces of the file from the origin. After the Front Door POP server receives a full or byte-ranges of the file requested, the Front Door edge server requests the file from the origin in chunks of 8 MB.

After the chunk arrives at the Front Door edge, it's cached and immediately served to the user. The Front Door then prefetches the next chunk in parallel. This prefetch ensures the content stays one chunk ahead of the user, which reduces latency. This process continues until the entire file gets downloaded (if requested), all byte ranges are available (if requested), or the client closes the connection. For more information on the byte-range request, see RFC 7233. The Front Door caches any chunks as they're received. The entire file doesn't need to be cached on the Front Door cache. Ensuing requests for the file or byte ranges are served from the Front Door cache. If not all the chunks are cached on the Front Door, prefetch is used to request chunks from the origin. This optimization relies on the ability of the origin server to support byte-range requests. If the origin server doesn't support byte-range requests, this optimization isn't effective.

Next steps