The FetchSFTP processor is deprecated in favor of the ListSFTP/FetchSFTP processors. The list/fetch model is works better in a NiFi cluster type configuration. Both the GetSFTP and ListSFTP processor should only ever be run on "primary node" only when used in a NiFi cluster. FetchSFTP should be configured to run on all nodes.
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That being said, the GetSFTP will retrieve up to the configured "Max Selects" in a single connection. The ListSFTP will return the filenames of all files in a single connection. (The 0 byte Flowfiles generated from listSFTP should be routed to a Remote Process Group that will redistribute those 0 Byte FlowFiles to all nodes in the cluster where FetchSFTP will retrieve the actual content.
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Regardless of how you retrieve the files, you are looking for a way to only process those files where you also retrieved the corresponding sha256 file. This can be accomplished using the Wait and Notify processors:
In the above flow I have all the retrieved data (both <datafile> and <datafile>.sha256 files) coming in to a RouteOnAttribute processor. I route all the <datafile>.sha256 FlowFiles to a Notify processor. (in my test I had 20 <datafile> files and only 16 corresponding <datafile>.sha256 files). The Notify processor is configured to write the ${filename} to a DistributeMapCache service that every node in my cluster can access. My Wait processor is then designed to check that same DistributedMapCache service looking for "${filename}.sha256". If a match is found the Wait processor will release the <datafile> to the success relationship for further processing in your dataflow. The Wait processor is also configured to wait on so long looking for a match. So you see in my example that after the length of time the 4 Flowfiles that did not have a matching sha256 filename in the cache were routed to "expired" relationship. Set expiration high enough to allot for the time needed to retrieve both files.
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Thank you,
Matt
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The FetchSFTP processor is deprecated in favor of the ListSFTP/FetchSFTP processors. The list/fetch model is works better in a NiFi cluster type configuration. Both the GetSFTP and ListSFTP processor should only ever be run on "primary node" only when used in a NiFi cluster. FetchSFTP should be configured to run on all nodes.
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That being said, the GetSFTP will retrieve up to the configured "Max Selects" in a single connection. The ListSFTP will return the filenames of all files in a single connection. (The 0 byte Flowfiles generated from listSFTP should be routed to a Remote Process Group that will redistribute those 0 Byte FlowFiles to all nodes in the cluster where FetchSFTP will retrieve the actual content.
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Regardless of how you retrieve the files, you are looking for a way to only process those files where you also retrieved the corresponding sha256 file. This can be accomplished using the Wait and Notify processors:
In the above flow I have all the retrieved data (both <datafile> and <datafile>.sha256 files) coming in to a RouteOnAttribute processor. I route all the <datafile>.sha256 FlowFiles to a Notify processor. (in my test I had 20 <datafile> files and only 16 corresponding <datafile>.sha256 files). The Notify processor is configured to write the ${filename} to a DistributeMapCache service that every node in my cluster can access. My Wait processor is then designed to check that same DistributedMapCache service looking for "${filename}.sha256". If a match is found the Wait processor will release the <datafile> to the success relationship for further processing in your dataflow. The Wait processor is also configured to wait on so long looking for a match. So you see in my example that after the length of time the 4 Flowfiles that did not have a matching sha256 filename in the cache were routed to "expired" relationship. Set expiration high enough to allot for the time needed to retrieve both files.
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Thank you,
Matt
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If you found this Answer addressed your original question, please take a moment to login and click "Accept" below the answer.
The FetchSFTP will make a separate connection for each file being retrieved. Concurrent Tasks will allow you to specify the number of concurrent connections allowing more then one file to retrieved per processor execution schedule (still one file per connection).
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Yes, HDF 3.1 will have all these goodies. Suggest skipping directly to HDF 3.1.2 which was just released since it has a loyt of fixes for some annoying bugs in HDF 3.1 and 3.1.1.
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You will have the option to use either an external REDIS configured how you like or an internal NiFi DistributedMapCacheServer with the WAIT and NOTIFY processors.
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The DistributedMapCacheServer provides the following configurations:
There is no TTL for the DistributedMapCacheServer option.
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There also isn't a processor that will dump out the current contents of the DistirbutedMapCacheServer, but you should be able to write a script that can do that for you. Here is an example script that is used to remove a cached entry:
https://gist.github.com/ijokarumawak/14d560fec5a052b3a157b38a11955772
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I do not know a lot about REDIS, but as an externally managed cache service, it probably will give you a lot more options as well as a cluster capability so you don't have a single point of failure like you would have with the DistributedMapCacheServer.
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Thank you,
Matt
