kaushik srinivas created LOGGING-201:
----------------------------------------
Summary: Syslog/Socket @ValidHost discards the appender on DNS
miss at config load; reconnect never runs (Kubernetes late Service DNS; relates
to LOG4J2-1047)
Key: LOGGING-201
URL: https://issues.apache.org/jira/browse/LOGGING-201
Project: Commons Logging
Issue Type: Bug
Affects Versions: 2.0.0
Reporter: kaushik srinivas
h3. Description
Log4j2 {{SyslogAppender}} (and Socket) validates {{host}} with {{@ValidHost}} →
{{InetAddress.getByName}} once at plugin build. If the name is syntactically
fine but not in DNS yet (typical Kubernetes: collector Service created after
the app JVM starts), configuration fail-closes:
* {{java.net.UnknownHostException}}
* {{The hostname is invalid}}
* {{field 'host' has invalid value '…'}}
* {{Null object returned for Syslog}}
* {{Unable to locate appender "SYSLOG"}}
{{{}reconnectionDelayMillis{}}}, {{{}immediateFail{}}},
{{{}ignoreExceptions{}}}, and {{AsyncAppender}} do not help: there is no
appender. {{monitorInterval}} only reloads if the config file mtime changes; it
does not retry DNS by itself.
This matches LOG4J2-1047 (2015, still Open): _When SyslogAppender can't find
inetAddress at startup, it will never try to reconnect._ Current 2.x surfaces
the failure at {{@ValidHost}} (LOG4J2-1755 introduced that constraint; it is
not a separate product bug).
Ask: do not use live DNS as “is this a valid host.” Reject empty/garbage
{{{}host{}}}; on {{{}UnknownHostException{}}}, still create the appender and
resolve on connect/reconnect (same idea as the 1047 patch).
h3. Steps to reproduce
# Log4j2 config with Syslog {{host}} = a DNS name that does not resolve,
{{{}protocol=TCP{}}}, optional {{{}reconnectionDelayMillis=5000{}}}.
# Start the JVM. Confirm the errors above; root logger has no SYSLOG.
# Publish the DNS name (e.g. create the Kubernetes Service). Do not restart,
do not change/touch the config file.
# Keep logging.
h3. Actual
SYSLOG never appears for that process. After DNS works,
{{InetAddress.getByName}} would succeed, but Log4j2 never calls it again.
h3. Expected
After DNS exists, Syslog connects (or retries) without a process restart or a
forced config-file reload. A typo in {{host}} can still fail fast.
h3. Environment
* Log4j2 2.x
* Kubernetes: {{host}} = {{*.svc.cluster.local}} not present at JVM start,
present seconds/minutes later
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
