update README with a couple of diagrams

README.md

@@ -1,22 +1,56 @@
 # Tansu
 
-[Tansu][github-com-tansu-io] is an Apache Kafka API compatible broker
-with PostgreSQL and S3 storage engines. Acting as a drop in replacement,
-existing clients connect to Tansu, producing and fetching messages.
-Written in 100% safe async 🦀 [Rust][rust-lang-org] 🚀.
+[Tansu][github-com-tansu-io] is a modern drop-in replacement for
+Apache Kafka. Without the cost of broker replicated storage for
+durability. Tansu is in **early** development, licensed under
+the [GNU AGPL][agpl-license]. Written in async 🚀
+[Rust][rust-lang-org] 🦀
+
+Tansu brokers are:
+
+- Kafka API compatible (exceptions: transactions and idempotent
+  producer)
+- Stateless with instant scaling up or down. No more planning and
+  reassigning partitions to a broker
+- Available with PostgreSQL or S3 storage engines
+
+For data durability:
+
+- S3 is designed to exceed [99.999999999% (11
+  nines)][aws-s3-storage-classes]
+- PostgreSQL with [continuous archiving][continuous-archiving]
+  streaming transaction logs files to an archive.
+
+Stateless brokers are cost effective, with no network replication and
+duplicate data storage charges.
+
+Stateless brokers do not have the ceremony of [Raft][raft-consensus]
+or [ZooKeeper][apache-zookeeper].
 
 ## S3
 
-Tansu with the S3 storage engine:
+You can have 3 brokers running in separate [Availability
+Zones][aws-regions-zones] for resilience:
+
+![Tansu S3](https://shortishly.com/assets/images/tansu-s3-2024-10-09.svg)
+
+Each broker is stateless. Brokers can come and go. Without affecting
+leadership of consumer groups. The leader and In-Sync-Replica is the
+broker serving your request. No more client broker ping pong.
+
+With Tansu there is no replication between brokers. The data transfer
+cost between the [Availability Zones][aws-regions-zones] is a $0 line
+item. There are $0 in duplicated storage charges.
 
-- Brokers do not replicate messages, instead relying on the underlying
-  storage for resilience.
-- Brokers do not require a consensus protocol (e.g., Raft or
-  Zookeeper), instead conditional PUTs are used to coordinate state.
-- Brokers are stateless.
-- All brokers are leaders.
+With stateless brokers, you can run Tansu in a [server-less
+architecture][wikipedia-serverless]:
 
-Note that, Tansu requires that the underlying S3 service support conditional
+![Tansu Lambda S3](https://shortishly.com/assets/images/tansu-lambda-s3-2024-10-09.svg)
+
+Spin up a broker for the duration of a Kafka API request. Then spin
+down. No more idle brokers.
+
+Tansu requires that the underlying S3 service support conditional
 PUT requests. While
 [AWS S3 does now support conditional writes][aws-s3-conditional-writes],
 the support is
@@ -25,11 +59,16 @@ To have stateless brokers we need to
 [use a compare and set operation][tigris-conditional-writes],
 which is not currently available in AWS S3.
 
-Much like the Kafka protocol, the open nature of the S3 protocol allows vendors
-to differentiate with different levels of service while retaining compatibility
-with the underlying API. We have tried [minio][min-io]
-and [tigis][tigris-conditional-writes], among a number of other vendors now supporting
-conditional put.
+Much like the Kafka protocol, the S3 protocol allows vendors to
+differentiate. Different levels of service while retaining
+compatibility with the underlying API. You can use [minio][min-io] or
+[tigis][tigris-conditional-writes], among a number of other vendors
+supporting conditional put.
+
+Tansu uses [object store][crates-io-object-store], providing a
+multi-cloud API for storage. There is an alternative option to use a
+[DynamoDB-based commit protocol, to provide conditional write support
+for AWS S3][object-store-dynamo-conditional-put] instead.
 
 ### configuration
 
@@ -51,7 +90,8 @@ Just bring minio up, without tansu:
 docker compose up -d minio
 ```
 
-The minio console should now be running on http://localhost:9001, login using
+The minio console should now be running on
+[http://localhost:9001](http://localhost:9001), login using
 the default user credentials of "minioadmin", with password "minioadmin". Follow
 the [bucket creation instructions][minio-create-bucket]
 to create a bucket called "tansu", and then
@@ -201,18 +241,30 @@ Consumer:
   -b localhost:9092
 ```
 
+## Feedback
+
+Please [raise an issue][tansu-issues] if you encounter a problem.
+
 ## License
 
 Tansu is licensed under the [GNU AGPL][agpl-license].
 
 [agpl-license]: https://www.gnu.org/licenses/agpl-3.0.en.html
+[apache-zookeeper]: https://en.wikipedia.org/wiki/Apache_ZooKeeper
+[aws-regions-zones]: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-regions-availability-zones.html
 [aws-s3-conditional-requests]: https://docs.aws.amazon.com/AmazonS3/latest/userguide/conditional-requests.html
 [aws-s3-conditional-writes]: https://aws.amazon.com/about-aws/whats-new/2024/08/amazon-s3-conditional-writes/
+[aws-s3-storage-classes]: https://aws.amazon.com/s3/storage-classes/
 [continuous-archiving]: https://www.postgresql.org/docs/current/continuous-archiving.html
+[crates-io-object-store]: https://crates.io/crates/object_store
 [github-com-tansu-io]: https://github.com/tansu-io/tansu
 [librdkafka]: https://github.com/confluentinc/librdkafka
 [min-io]: https://min.io
+[minio-create-access-key]: https://min.io/docs/minio/container/administration/console/security-and-access.html#id1
+[minio-create-bucket]: https://min.io/docs/minio/container/administration/console/managing-objects.html#creating-buckets
+[object-store-dynamo-conditional-put]: https://docs.rs/object_store/0.11.0/object_store/aws/struct.DynamoCommit.html
+[raft-consensus]: https://raft.github.io
 [rust-lang-org]: https://www.rust-lang.org
+[tansu-issues]: https://github.com/tansu-io/tansu/issues
 [tigris-conditional-writes]: https://www.tigrisdata.com/blog/s3-conditional-writes/
-[minio-create-bucket]: https://min.io/docs/minio/container/administration/console/managing-objects.html#creating-buckets
-[minio-create-access-key]: https://min.io/docs/minio/container/administration/console/security-and-access.html#id1
+[wikipedia-serverless]: https://en.wikipedia.org/wiki/Serverless_computing