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Apache Kafka @duffleit THE HARD PARTS

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David Leitner @duffleit Coding Architect david@squer.at @duffleit

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The Basics Cluster Node A Node B Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C''

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The Basics Cluster Node A Node B Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C'' Producer

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The Basics Cluster Node A Node B Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C'' Consumer Consumer

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The Basics Cluster Node A Node B Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C'' Consumer Consumer The number of partitions is the limiting factor for consumer instances.

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The Basics Cluster Node A Node B Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C'' Consumer Consumer The number of partitions is the limiting factor for consumer instances. User: Bob User: Alice User: Tim selection of partition: = hash(key) % #ofpartitions User: Bob

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The Basics Cluster Node A Node B Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C'' Consumer Consumer The number of partitions is the limiting factor for consumer instances. Partition D Partition '' Partition ' User: Bob User: Alice User: Tim selection of partition: = hash(key) % 3 to 4 User: Bob User: Bob User: Bob User: Alice Topic.v2

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The Basics Cluster Node A Node B Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C'' Consumer Consumer The number of partitions is the limiting factor for consumer instances. Select is wisely & over partition a bit. Partition D Partition '' Partition ' User: Bob User: Alice User: Tim selection of partition: = hash(key) % 3 to 4 User: Bob User: Bob User: Bob User: Alice Topic.v2 Select something that can be devided by multipe numbers. e.g. 6, 12, 24, ...

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The Basics Topic: UserChanges User: Bob User: Alice User: Tim User: Bob User: Bob log.cleanup.policy: delete

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The Basics Topic: UserChanges User: Bob User: Alice User: Tim User: Bob User: Bob log.cleanup.policy: delete 2 weeks or some size

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The Basics Topic: UserChanges User: Bob User: Alice User: Tim User: Bob User: Bob log.cleanup.policy: delete 2 weeks

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The Basics Topic: UserChanges User: Bob User: Alice User: Tim User: Bob User: Bob log.cleanup.policy: compact we only keep the latest record for a specific key.

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The Basics Topic: UserChanges User: Bob User: Alice User: Tim User: Bob User: Bob log.cleanup.policy: compact we only keep the latest record for a specific key. How Kafka Stores Data userchanges.active.segment 📄 userchanges.segment.1 userchanges.segment.2 log.segment.bytes = 1GB Active Compaction ⚙ Compaction ⚙

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The Basics Topic: UserChanges User: Bob User: Alice User: Tim User: Bob User: Bob log.cleanup.policy: compact we only keep the latest record for a specific key. How Kafka Stores Data userchanges.active.segment 📄 userchanges.segment.1 userchanges.segment.2 log.segment.bytes = 1GB Active Compaction ⚙ Compaction ⚙

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The Basics Topic: UserChanges User: Bob User: Alice User: Tim User: Bob User: Bob log.cleanup.policy: compact we only keep the latest record for a specific key. How Kafka Stores Data userchanges.active.segment 📄 userchanges.segment.1 userchanges.segment.2 log.segment.bytes = 1GB Active Compaction ⚙ Compaction ⚙ log.segment.ms = 1week Especially in GDPR related usecases think explicitly about segement-size and roll-time.

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The Basics Topic: UserChanges User: Bob User: Alice User: Tim User: Bob User: Bob log.cleanup.policy: compact Tombstone: Tim delete.retention.ms = 1day Slow Consumer needs more than one day to read all events from the topic that starts new. Tombstone: Tim

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The Basics Topic: UserChanges User: Bob User: Alice User: Tim User: Bob User: Bob log.cleanup.policy: compact Tombstone: Tim delete.retention.ms = 1day Slow Consumer needs more than one day to read all events from the topic that starts new. User: Tim Keep delete.retention in sync with the given topic retention.

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The Basics Cluster Node A Node B Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C''

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The Basics Cluster Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C'' Node B Node A Node F Node E Node D AZ 1 AZ 2

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The Basics Cluster Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C'' Node B Node A Node F Node E Node D AZ 1 AZ 2 Partition D Partition E Partition F Partition D' Partition D'' Partition E' Partition E'' Partition F' Partition F'' KIP-36: Rack aware replica assignment

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Cluster The Basics Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C'' Node B Node A Node F Node E Node D AZ 1 AZ 2 Partition D Partition E Partition F Partition D' Partition D'' Partition E' Partition E'' Partition F' Partition F'' KIP-36: Rack aware replica assignment

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Multi Region

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Cluster Multi Region? Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Node B Node A Node F Node E Node D Region 1 Region 2 Partition D' Partition D'' Partition E' Partition E'' Partition F' Partition F'' Partition A' Partition A'' Partition B' Partition B'' Partition C' Partition C'' Partition D Partition E Partition F Usually the latency between multiple regions is to big to span a single cluster over it

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Cluster Region West Cluster Region East Multi Region? Node C Producer Consumer Consumer Consumer Group Topic Partition A Partition B Partition C Node B Node A Node F Node E Node D Region 1 Region 2 Partition D' Partition D'' Partition E' Partition E'' Partition F' Partition F''

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Cluster Region West Cluster Region East Multi Region? Node C Producer Consumer Consumer Consumer Group Topic A B C Node B Node A Node F Node E Node D Region 1 Region 2 A B C

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Cluster Region West Cluster Region East Multi Region? Node C Producer East Consumer Consumer Consumer Group Topic A B C Node B Node A Node F Node E Node D Region 1 Region 2 A B C Producer West

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Cluster Region West — "west" Cluster Region East — "east" Multi Region? Node C Producer East Consumer Consumer Consumer Group Topic A B C Node B Node A Node F Node E Node D Region 1 Region 2 A B C Producer West Mirror Maker 2 east.C west.C *.C Ordering Guarantees?!

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@duffleit Order is Guaranteed in a single Partition. Are you sure?

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@duffleit Producer Partition max.in.flight.requests.per.connection = 5 Message A Message B Message A retry Message B Message A retries = MAX_INT

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@duffleit Producer Partition max.in.flight.requests.per.connection = 5 Message A Message B Message A retry Message B Message A Legacy Solution: max.in.flight.requests.per.connection = 1 State-of-the-Art Solution: enable.idempotence = true retries = MAX_INT max.in.flight.requests.per.connection = 5 acks = all SEQ#: 1 SEQ#: 2 OutOfOrderSequenceException SEQ#: 2 If you don't want to set your retries to invinite prefer "delivery.timeout.ms" over "retries".

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Node A Node B Node C Topic Partition A Partition B Partition C Partition C' Partition B'' Partition A' Partition C'' Partition B' Partition A'' Producer acks = none acks = 1 acks = all min.insync.replicas = 3 @duffleit

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Node A Node B Node C Topic Partition A Partition B Partition C Partition C' Partition B'' Partition A' Partition C'' Partition B' Partition A'' Producer acks = none acks = 1 acks = all min.insync.replicas = 2 @duffleit

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min.insync.replicas = 2 Node A Node B Node C Topic Partition A Partition B Partition C Partition C' Partition B'' Partition A' Partition C'' Partition B' Partition A'' Producer acks = all @duffleit CAP Theorem Consistency Availabiltiy Paritioning ❌ min.insync.replicas++ min.insync.replicas--

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min.insync.replicas = 3 Node A Node B Node C Topic Partition A Partition B Partition C Partition C' Partition B'' Partition A' Partition C'' Partition B' Partition A'' Producer acks = all @duffleit CAP Theorem Consistency Availabiltiy Paritioning ❌ min.insync.replicas++ min.insync.replicas--

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min.insync.replicas = 3 Node A Node B Node C Topic Partition A Partition B Partition C Partition C' Partition B'' Partition A' Partition C'' Partition B' Partition A'' Producer acks = all @duffleit CAP Theorem Consistency Availabiltiy Paritioning ❌ min.insync.replicas++ min.insync.replicas--

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min.insync.replicas = 2 Node A Node B Node C Topic Partition A Partition B Partition C Partition C' Partition B'' Partition A' Partition C'' Partition B' Partition A'' Producer acks = all @duffleit CAP Theorem Consistency Availabiltiy Paritioning ❌ min.insync.replicas++ min.insync.replicas--

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min.insync.replicas = 2 Node A Node B Node C Topic Partition A Partition B Partition C Partition C' Partition B'' Partition A' Partition C'' Partition B' Partition A'' Producer acks = all @duffleit CAP Theorem Consistency Availabiltiy Paritioning ❌ min.insync.replicas++ min.insync.replicas-- Possible Data Loss There is no "ad-hoc fsync" by default. Can be configured via "log.default.flush.interval.ms"

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@duffleit Keep in mind that rack assignment is ingnored for insync replicas. Node C Node B Node A Node D Node E Node F AZ 1 AZ 2 Text . . . . . replicas=6 min.insync.replicas = 4

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@duffleit Keep in mind that rack assignment is ingnored for insync replicas. Node C Node B Node A Node D Node E Node F AZ 1 AZ 2 Text . . . . replicas=5 min.insync.replicas = 4 fail on > 1

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@duffleit Keep in mind that rack assignment is ingnored for insync replicas. Node C Node B Node A Node D Node E Node F Node G Node H Node I AZ 1 AZ 2 AZ 3 Text . . . . . . . . replicas=9 min.insync.replicas = 7

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@duffleit @duffleit Let's talk about Lost Messages

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@duffleit Partition Message A Consumer Message B Message C enable.auto.commit=true auto.commit.interval.ms=5_SEC

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@duffleit Partition Message A Consumer Message B Message C enable.auto.commit=true auto.commit.interval.ms=5_SEC Auto-Commit: A,B,C

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@duffleit Partition Message D Consumer enable.auto.commit=true auto.commit.interval.ms=5_SEC Message A Message B Message C enable.auto.commit=false

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@duffleit

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Producer Stream Consistency Kafka, and "Non-Kafka". Transaction to achieve Message

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Producer Stream Consistency Kafka, and "Non-Kafka". Transaction to achieve Message Message

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Producer Stream Consistency Kafka, and "Non-Kafka". Transaction to achieve Message Message Producer Consumers Achieve Exactly Once Semantics. Transaction to achieve Message

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Producer Stream Consistency Kafka, and "Non-Kafka". Transaction to achieve Message Message Producer Consumers Achieve Exactly Once Semantics. Transaction to achieve Message Exactly Once. Atomicity between multipe Topic Operations. Transaction to achieve Transactions Balances Producer Message

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Producer Stream Consistency Kafka, and "Non-Kafka". Transaction to achieve Message Message Producer Consumers Achieve Exactly Once Semantics. Transaction to achieve Message Exactly Once. Atomicity between multipe Topic Operations. Transaction to achieve Transactions Balances Producer Message Message

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@duffleit Onboarding UserUpdate Stream 💥 ✅

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@duffleit Onboarding UserUpdate Stream User UserEvents CDC Outbox Pattern ✅

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@duffleit Onboarding UserUpdate Stream ✅ User Listen to yourself Pattern.

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@duffleit Onboarding UserUpdated (age: 21) Stream UserUpdated (age: 21) Advertisment User (age: 21) User (age: 21) EventSourcing

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@duffleit Onboarding UserUpdated (age: 22) Stream UserUpdated (age: 21) Advertisment User (age: 21) User (age: 21) UserUpdated (age: 22) EventSourcing

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@duffleit Onboarding UserUpdated (age: 22) Stream UserUpdated (age: 21) Advertisment User (age: 22) User (age: 22) UserUpdated (age: 22) UserUpdated (age: 23) EventSourcing

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@duffleit Onboarding UserUpdated (age: 22) Stream Global EventSourcing UserUpdated (age: 21) Advertisment User (age: 22) User (age: 22) UserUpdated (age: 22) UserUpdated (age: 23) 👻 if often breaks information hiding & data isolation.

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Stream @duffleit UpdateUser (age: 21) Stream Local EventSourcing UserAgeChanged (age: 21) UserUpdated (age: 21) Onboarding 🔒 👻 💅

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Producer Producer Stream Consumers Achieve Exactly Once Semantics. Transaction to achieve Consistency Kafka, and "Non-Kafka". Transaction to achieve Atomicity between multipe Topic Operations. Transaction to achieve Transactions Balances Producer Message Message Message Outbox Pattern Listen to Yourself Local Eventsourcing Message

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@duffleit "Kafka Transactions" Producer Consumers Producer Producer Consumers Consumers Stream Processor Stream Processor Stream Processor enable.idempotence = true isolation.level = read_committed Deduplication Inbox

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Producer Stream Achieve Exactly Once Semantics. Transaction to achieve Consistency Kafka, and "Non-Kafka". Transaction to achieve Atomicity between multipe Topic Operations. Transaction to achieve Message Outbox Pattern Listen to Yourself Local Eventsourcing Deduplication Inbox Idempotency Producer Consumers Transactions Balances Producer Message Message Message

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Transfers Payment Service Alice -> Bob Alice -10€ Bob +10€ Transaction_Coordinator

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Transfers Payment Service Alice -> Bob Alice -10€ Bob +10€ __transaction_state Transaction: ID __consumer_offset payments: 1 P1 P1 P2 Transfers P3 P2 P3 C C C C isolation.level=read_committed

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Transfers Payment Service Alice -> Bob Alice -10€ __transaction_state Transaction: ID __consumer_offset payments: 1 P1 P1 P2 Transfers P3 P2 isolation.level=read_committed Service A A A Transaction: ID2

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Producer Stream Achieve Exactly Once Semantics. Transaction to achieve Consistency Kafka, and "Non-Kafka". Transaction to achieve Atomicity between multipe Topic Operations. Transaction to achieve Message Outbox Pattern Listen to Yourself Listen to yourself Deduplication Inbox Idempotency Producer Consumers Transactions Balances Producer Message Message Message Kafka's Exactly-Once Semantics Outbox Pattern

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@duffleit

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@duffleit Producer Consumers Topic 📜 📜 Producer Producer Producer Producer Producer Producer Producer Consumers Consumers Consumers Consumers Consumers Consumers Consumers Topic Topic Topic Topic Topic Topic Topic

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Consumers Consumers Consumers Consumers Consumers Consumers Consumers Producer Producer Producer Producer Producer Producer Producer @duffleit Producer Consumers Topic 📜 📜 Topic Topic Topic Topic Topic Topic Topic

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@duffleit Producer Consumers Topic Schema Registry Faulty Message Producer Producer Producer Producer Producer Producer Producer Broker Side Validation, FTW

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@duffleit Producer Consumers Topic Schema Registry Faulty Message Broker Side Validation 🤚 Deserialization on Broker 😱 MagicByte SubjectId Payload ✅ Check if MagicByte Exists. ✅ Check if SubjectId is Valid. ✅ Check if Payload Matches Schema. The more to the right, the more expensive it gets.

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@duffleit squer.link/broker-side-valdiation-sidecar

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@duffleit Cluster Node A Node B Node C Go Proxy Go Proxy Go Proxy ⏳ ⏳ ⏳

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@duffleit Cluster Node A Node B Node C Go Proxy Go Proxy Go Proxy Go Proxy Go Proxy Go Proxy Race Condition We can no longer guarantee ordering.

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@duffleit squer.link/broker-side-valdiation-sidecar

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Ok, Lets sum up. @duffleit

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@duffleit Multi AZ, Multi Region, Multi Cloud Consistency vs. Availability Disable Autocommit! Different Options to Achieve Transactional Guarantees in Kafka Broker Side Schema Validation Segment Size Portion Size: "over-partition a bit" and 200+ more Configuration Properties. What we have seen 👀

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@duffleit Multi AZ, Multi Region, Multi Cloud Consistency vs. Availability Disable Autocommit! Different Options to Achieve Transactional Guarantees in Kafka Broker Side Schema Validation Segment Size Portion Size: "over-partition a bit" and 200+ more Configuration Properties. What we have seen 👀 We were able to handle them, so are you. 💪

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David Leitner @duffleit Coding Architect david@squer.at @duffleit