Disclaimer I am the CEO of Eris Industries.

Firstly, we are not doing centralized blockchains, we're doing permissioned blockchains which work most efficiently when actors within the system have been identified. These blockchains are simply one element of the Eris Blockchain Application platform we are developing.

Comparing a smart contract enabled blockchain to a distributed messaging broker is a difficult proposition as they are very much apples and oranges in their capabilities, usage, and goals.

That said let me give it a go.

## Similarities

* Kafka and eris:db both work on a distributed model * Kafka and eris:db both are inherently scalable and persist their data * Kafka and eris:db both include a distributed messaging layer optimized for their system which is not http

## Differences

* eris:db persists using merkle-ized encoding schemes with all data having been digitally signed via a node using an ECC-PKI and verified by a logic gateway (known commonly as a smart contract) prior to being persisted -- eris:db further builds logs into blocks and chains those together using traditional blockchain techniques; kafka uses a relatively sophisticated, but not inherently as verifiable "traditional" logging mechanism * eris:db, as with any blockchain, includes a [fork choice rule](https://eng.erisindustries.com/blockchain/2015/04/30/on-bloc...) for resolving differences within the nodes on the network as to prior history as well as adding a layer of byzantine fault tolerance; from my (admittedly cursory) overview of kafka while it is distributed it is not byzantine fault tolerant * kafka is fast and meant as a near real time message broker; eris:db is not built for speed and sacrifices some availability for consistency

## Overall

Message brokers are great complements to blockchains actually as they can provide an additional speed layer for messages which blockchains are not particularly good at.

user:	compleat-ang
created:	December 18, 2014
karma:	2
about:	[ my public key: https://keybase.io/compleatang; my proof: https://keybase.io/compleatang/sigs/mRvZ40LUUI3hVG3b3maF2EOBLjfmi4wIgob5a8TOuNM ]