Warning: This document is for an old version of zrepl. The main version is master.

Logging

zrepl uses structured logging to provide users with easily processable log messages.

Logging outlets are configured in the global section of the main configuration file. Check out config/samplesrandom/logging.yml for an example on how to configure multiple outlets:

global:
  logging:

    - outlet: OUTLET_TYPE
      level: MINIMUM_LEVEL
      format: FORMAT

    - outlet: OUTLET_TYPE
      level: MINIMUM_LEVEL
      format: FORMAT

    ...

jobs: ...

Default Configuration

By default, the following logging configuration is used

global:
  logging:

    - outlet: "stdout"
      level:  "warn"
      format: "human"

Attention

Output to stderr should always be considered a critical error. Only errors in the logging infrastructure itself, e.g. IO errors when writing to an outlet, are sent to stderr.

Building Blocks

The following sections document the semantics of the different log levels, formats and outlet types.

Levels

Level SHORT Description
error ERRO immediate action required
warn WARN symptoms for misconfiguration, soon expected failure, etc.
info INFO explains what happens without too much detail
debug DEBG tracing information, state dumps, etc. useful for debugging.

Incorrectly classified messages are considered a bug and should be reported.

Formats

Format Description
human emphasizes context by putting job, task, step and other context variables into brackets before the actual message, followed by remaining fields in logfmt style|
logfmt logfmt output. zrepl uses this Go package.
json JSON formatted output. Each line is a valid JSON document. Fields are marshaled by encoding/json.Marshal(), which is particularly useful for processing in log aggregation or when processing state dumps.

stdout Outlet

Parameter Comment
outlet stdout
level minimum log level
format output format

Writes all log entries with minimum level level formatted by format to stdout.

Can only be specified once.

syslog Outlet

Parameter Comment
outlet syslog
level minimum log level
format output format
retry_interval Interval between reconnection attempts to syslog (default = 0)

Writes all log entries formatted by format to syslog. On normal setups, you should not need to change the retry_interval.

Can only be specified once.

tcp Outlet

Warning

The TCP outlet is not fully asynchronous and blocks the calling goroutine when it cannot connect. Currently it should only be used for local connections that are guaranteed to not fail / be slow. This issue is tracked in issue #26

Parameter Comment
outlet tcp
level minimum log level
format output format
net tcp in most cases
address remote network, e.g. logs.example.com:10202
retry_interval Interval between reconnection attempts to address
tls TLS config (see below)

Establishes a TCP connection to address and sends log messages with minimum level level formatted by format.

If tls is not specified, an unencrypted connection is established.

If tls is specified, the TCP connection is secured with TLS + Client Authentication. This is particularly useful in combination with log aggregation services that run on an other machine.

Parameter Description
ca PEM-encoded certificate authority that signed the remote server’s TLS certificate
cert PEM-encoded client certificate identifying this zrepl daemon toward the remote server
key PEM-encoded, unencrypted client private key identifying this zrepl daemon toward the remote server

Note

zrepl uses Go’s crypto/tls and crypto/x509 packages and leaves all but the required fields in tls.Config at their default values. In case of a security defect in these packages, zrepl has to be rebuilt because Go binaries are statically linked.