Home > openstack, zero-VM > How zerocloud resolves zerovm app and input file located on different nodes

How zerocloud resolves zerovm app and input file located on different nodes

Suppose, I have a swift cluster of 3 nodes (node1, node2, node3). I have a zerovm app (zapp)  that uses data.txt as an input file.

Now, if the zerovm app is deployed in node1, input file is stored in node2, how the request to execute the zapp is resolved in terms of forwarding request to which object server?

To explain the situation, the proxy server may discover that the zapp and input file are on different nodes. It retrieves actual location (host address and absolute path on the filesystem) of the files and  one of the following may occur:

1. proxy-server forwards the request where the input file is – node2 in this case. Node2 retrieves zapp file from node1, and zerovm is launched at node2.

2. proxy-server forwards the request where the zapp is – node1 in this case. Node1 retrieves input file (data.txt) from node2 and zerovm is launched at node1.

In fact, option 1. make more sense in the sense that input file can be larger than the zapp. Yes, that’s what will happen.

By default it will decide using following logic: first channel with read-only data and not the script/executable/image will win. There is a more complex behaviour when there are writeable channels and other constructs.

On the other hand, you can always co-locate everything with specific channel by using “attach” property of the node. I.e. “attach”: “stdin” will attach everything to the node where the “stdin” channel is located.

 

Reference:

1. https://groups.google.com/forum/#!topic/zerovm/tpbiNDeHw_I

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Categories: openstack, zero-VM
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