As of V3.4, the |
The FileBackedHTTPMetadataProvider loads a metadata file from an HTTP server. The provider periodically reloads the metadata file if necessary.
The FileBackedHTTPMetadataProvider is used with remote metadata. See the MetadataManagementBestPractices topic for more information. |
The FileBackedHTTPMetadataProvider spools the metadata contents to a local backing file, which is used at startup. As of v3.3.0, the backing file is only used at startup. A refresh operation never consults the backing file since the latter can't possibly represent newer metadata than what is already cached in memory.
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The <MetadataProvider> element and the type FileBackedHTTPMetadataProvider are defined by the urn:mace:shibboleth:2.0:metadata schema, which can be located at http://shibboleth.net/schema/idp/shibboleth-metadata.xsd.
Any of the Common Attributes, the Reloading Attributes, or the HTTP Attributes may be configured. In addition, a FileBackedHTTPMetadataProvider has a few attributes of its own, some of which are required:
| Name | Type | Default | Description |
|---|---|---|---|
metadataURL | URL | required | The URL that the metadata is served from. |
backingFile | File specificaton | required | Specifies where the backing file is located. If the remote server is unavailable at startup, the backing file is loaded instead. |
initializeFromBackupFile 3.3 | Boolean | true | Flag indicating whether initialization should first attempt to load metadata from the backup file. If true, foreground initialization will be performed by loading the backing file, and then a refresh from the remote HTTP server will be scheduled to execute in a background thread, after a configured delay. This can improve IdP startup times when the remote HTTP file is large in size. |
backupFileInitNextRefreshDelay 3.3 | Delay (ISO8601 format) | PT5S (5 seconds) | Delay duration after which to schedule next HTTP refresh when initialized from the backing file. |
For a FileBackedHTTPMetadataProvider, the HTTP Connection Attributes have the following default timeout values:
| Name | Default |
|---|---|
connectionRequestTimeout | PT60S (60 seconds) |
connectionTimeout | PT60S (60 seconds) |
socketTimeout | PT60S (60 seconds) |
Since the batch metadata refresh process runs in a background thread, a browser user will not notice such a delay.
By default, a FileBackedHTTPMetadataProvider does not cache metadata (httpCaching="none"). Unless you've read the code or otherwise know what you're doing, do not override this setting.
Regardless of the value of the httpCaching attribute, a FileBackedHTTPMetadataProvider always issues HTTP conditional GET requests. For this reason, a custom HTTP client is seldom needed.
Out of the box, a |
Any of the following child elements may be specified (in order).
| Name | Cardinality | Description |
|---|---|---|
<MetadataFilter> | 0 or more | A metadata filter applied to candidate metadata as it flows through the metadata pipeline |
<TLSTrustEngine> 3.1 | 0 or 1 | A custom TrustEngine used to evaluate TLS server certificates. This element conflicts with and is overridden by the deprecated tlsTrustEngineRef attribute. |
The former is common to all metadata providers while the latter is common to all HTTP metadata providers. The FileBackedHTTPMetadataProvider type has no child elements of its own.
A typical use of FileBackedHTTPMetadataProvider is to load (and periodically reload) a metadata aggregate from a remote source via HTTP:
It's also possible to load (and periodically reload) a single entity descriptor:
In any case, the metadata is loaded (and reloaded) out-of-band and therefore will not interfere with any SAML protocol exchange.
See also Troubleshooting.
A FileBackedHTTPMetadataProvider loads (and reloads) metadata in the background, independent of normal IdP operation. The frequency of metadata refresh is influenced by the Reloading Attributes. In particular, the minRefreshDelay and maxRefreshDelay attributes strongly influence the frequency of metadata refresh. Any cacheDuration and validUntil attributes in the metadata itself also influence the process.
Large metadata files consume a significant amount of memory, especially during the reload process (when the IdP must have both the old and the new metadata at hand). Precise memory requirements depend on overall IdP load and other deployment-specific factors but large metadata files (such as those distributed by some federations) may require a system configured with 2GB of memory or more. Ask your federation operator for specific recommendations.
Although metadata refresh can put significant load on the system, all refresh operations are performed in the background, independent of normal IdP operation. Assuming there are no resource limiting factors (such as inadequate memory), end users will not notice the effects of metadata refresh.
There are at least two things you can do to help minimize the impact of the metadata refresh process: 1) install and configure adequate memory on your system, and 2) customize the frequency of metadata refresh for optimal performance. In any case, the FileBackedHTTPMetadataProvider implementation has two features that positively affect metadata refresh: background processing and HTTP conditional GET. Neither of these features is configurable, however, so there is nothing further you need to do beyond the two items mentioned above.
A conforming server will respond to an HTTP conditional GET request (RFC 7232) with a 304 (Not Modified) status code if the target resource has not changed since the last time it was requested. Note that a 304 response does not include a response body, which is more efficient than the corresponding 200 response (especially for large metadata files). More importantly, due to the manner in which the FileBackedHTTPMetadataProvider is implemented, the IdP can safely ignore a 304 response, which precludes the need to redundantly process the metadata. For large signed metadata files, the savings can be quite significant.
To influence the frequency of metadata refresh, configure the following attributes on a FileBackedHTTPMetadataProvider instance: minRefreshDelay, maxRefreshDelay, and refreshDelayFactor. Optimal values for these attributes depend on 1) whether or not the server supports HTTP conditional GET, 2) the life cycle of metadata published on the server, and possibly other factors. Ask the metadata publisher for recommended best practices with respect to published metadata.
The backing file is only used at startup. If the remote server is unavailable at startup, the backing file is loaded instead and all the configured filters are run on the backing file. If a single filter fails, the backing file is not loaded. For example, if the provider contains a SignatureValidationFilter but the signature on the backing file can not be verified, the entire load operation fails.
If a FileBackedHTTPMetadataProvider is unable to load the backing file at startup, and the failFastInitialization attribute on the provider is set to true (default: true), the metadata initialization process will halt. Additionally, if the service property idp.service.metadata.failFast is set to true (default: false), the IdP as a whole will fail to initialize.
Yes, it does so internally, though not across restarts of the system (it will not have a cache tag at startup but will maintain one in memory after the initial request for metadata and do conditional GETs until the next restart).