[krat0sprakhar]

> The new manifest format in Docker 1.10 is a full Merkle DAG, and all the downloaded content is finally content addressable.

Can someone elaborate on this a bit more? From a CS point-of-view, sounds like a problem where a data structure came in handy but I'm not sure what it solves. Thanks!

[kordless]

A simple immutable data structure can be implemented with a Merkle DAG. Merkle tree leaves store hashes of previous nodes and DAGs are directed graphs that don't loop around. Examples include simple blockchains. These structure provides immutable, versioned control of information. Containers are immutable, or like to think they are at least, so blockchains are an obvious thing to use in conjunction with deployments of said containers. At least that's what I keep telling everyone.

[tlrobinson]

Do you literally mean a proof-of-work backed blockchain (like Bitcoin), or something more like git, which has a similar structure to a blockchain without the consensus mechanism?

I don't see how the former would be useful to someone deploying containers, but interested to hear your thoughts in either case.

[_ikke_]

From the blogpost:

> Image IDs now represent the content that is inside an image, in a similar way to how Git commit hashes represent the content inside commits.

[tlrobinson]

I was referring to the second part of the comment:

"Containers are immutable, or like to think they are at least, so blockchains are an obvious thing to use in conjunction with deployments of said containers. At least that's what I keep telling everyone."

[mikekchar]

I'm pretty sure they mean that they are using Merkle DAGs. A blockchain is a Merkle DAG. The proof-of-work algorithm in Bitcoin is an algorithm for deciding how a node gets added to the blockchain. Depending on how you look at it, that algorithm is not part of what makes it a "blockchain".

Admittedly people are sloppy about how they use the term "blockchain". I would prefer that people use the term Merkle DAG and forget the term "blockchain" altogether, but I think we are stuck with "blockchain" ;-)

[kordless]

"People" are also sloppy about how they use the term "cloud", yet the world goes on with that concept in hand applying it to everything in site, often times in irritating ways. "Blockchain" is now a thing people can hold in their hand as a way to visualize the concept of a nearly immutable data store. That idea of storing something in an immutable way represents a shift in the way we can think about system's design. Calling it a "Merkle DAG" isn't going to kick off that insight any better than using "blockchain", but remembering what it really is and drawing the distinction with the right people can be immensely useful when trying to implement the insight.

[kordless]

Blockchains don't have to contain proof-of-work as long as the values in the chain itself aren't valued in and of themselves over longer time periods. In Bitcoin, a cryptocurrency built using a blockchain, the values represent debt owed to someone in exchange for a real world item, and that debt stays active for the life of the entry. There are a slew of proof-of-somethings that allow blockchains to become cryptocurrencies. I don't exactly ascribe to these ideas of value store as related to compute provisioning, but I suppose there could be some actions which might benefit from it, such as certain types of licensing.

That said, triggering provisioning using cryptocurrencies is likely to be a thing at some point.

[gcr]

Is a git repository one implementation of a Merkel DAG?