Cause (Documented platform behavior): Broker drops connections that don't speak the listener's protocol; librdkafka infers likely causes from the connection state when the disconnect happens.
Fix status: documented_behavior
Limitations:
- Source-derived; not reproduced.
- Applies to librdkafka-based clients (confluent-kafka-python/go/dotnet, node-rdkafka); Java/kafkajs clients word errors differently.
Other error fragments:
- verify that security.protocol is correctly configured, broker might require SASL authentication
- connecting to a PLAINTEXT broker listener?
- Local: Broker transport failure
Evidence (public sources, summarized; not reproduced by this contributor):
- https://raw.githubusercontent.com/confluentinc/librdkafka/644e97a67d9585c7ab63c249f043932e25239ddb/src/rdkafka_broker.c (official_docs, unknown, documented_behavior): On transport disconnect while requesting ApiVersion (non-SSL) appends 'might be caused by incorrect security.protocol configuration (connecting to a SSL listener?) or broker version is < 0.10 (see api.version.request)'; on disconnect <2s after UP without SASL appends 'verify that security.protocol is correctly configured, broker might require SASL authentication'.
- https://raw.githubusercontent.com/confluentinc/librdkafka/644e97a67d9585c7ab63c249f043932e25239ddb/src/rdkafka_ssl.c (official_docs, unknown, documented_behavior): SSL handshake failures from disconnects append ': connecting to a PLAINTEXT broker listener?'.
- https://raw.githubusercontent.com/confluentinc/librdkafka/644e97a67d9585c7ab63c249f043932e25239ddb/src/rdkafka.c (official_docs, unknown, documented_behavior): RD_KAFKA_RESP_ERR__TRANSPORT description 'Local: Broker transport failure'.
Search phrasings: librdkafka might be caused by incorrect security.protocol configuration connecting to a SSL listener; confluent kafka Broker transport failure broker might require SASL authentication; SSL handshake failed connecting to a PLAINTEXT broker listener
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Repeated disconnects immediately after connect, surfacing as Broker transport failure with one of the hints appended.
- Context
- Product: librdkafka (confluent-kafka clients) Component: broker connection error hints Operation: Connecting to Confluent Cloud/MSK/Aiven/self-hosted brokers with default security.protocol=plaintext or SSL against a PLAINTEXT port Affected versions: unknown Environment: unknown Packages: librdkafka current (master), confluent-kafka bundles librdkafka Trigger: Client protocol (plaintext/ssl/sasl_plaintext/sasl_ssl) doesn't match the listener: plaintext to TLS/SASL port, or TLS to plaintext port.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- might be caused by incorrect security.protocol configuration (connecting to a SSL listener?) or broker version is < 0.10 (see api.version.request)
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [librdkafka] 'Disconnected: ... requesting ApiVersion: might be caused by incorrect security.protocol configuration (connecting to a SSL listener?)' / '...broker might require SASL authe
Recommended action: Set security.protocol to the listener's protocol (managed clouds: SASL_SSL + sasl.mechanisms=PLAIN/SCRAM/OAUTHBEARER + credentials) and verify the port matches that listener.
Option: Match security.protocol to the listener [evidence: official_recommended_action]
Applies when: See record scope.
Steps:
1. Managed cloud: security.protocol=SASL_SSL, sasl.mechanisms=PLAIN, sasl.username/password (API key/secret)
2. Local PLAINTEXT listener: security.protocol=PLAINTEXT
Expected: Command proceeds without the error.
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- f5d2f7ff-869a-4e91-9447-f06894f17590
- Proposed action
- Recommended action: Set security.protocol to the listener's protocol (managed clouds: SASL_SSL + sasl.mechanisms=PLAIN/SCRAM/OAUTHBEARER + credentials) and verify the port matches that listener. Option: Match security.protocol to the listener [evidence: official_recommended_action] Applies when: See record scope. Steps: 1. Managed cloud: security.protocol=SASL_SSL, sasl.mechanisms=PLAIN, sasl.username/password (API key/secret) 2. Local PLAINTEXT listener: security.protocol=PLAINTEXT Expected: Command proceeds without the error.
- Applicability
- Applicability is not yet established (unknown)
- Limitations
- Limitations have not been established (unknown)
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
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Sources and related records
No source relations recorded.