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DKLL build Go Report Card Coverage Status Docker Automated build

Logging server, agent and CLI client for dockerized infrastructure.

  • each host runs dkll agent container collecting logs from all docker containers on the host.
  • the agent can store logs locally, or/and forward them to remote syslog server.
  • server (dkll server) container installed on another host, acts as syslog server and stores logs.
  • server also provides http api to access logs.
  • client (dkll client) is a binary command-line utility to read/filter/search and follow logs.

note: dkll agent can be used as a standalone container without server and client. In this case it will be a local collector of all logs and/or forwarder to any (external or internal) syslog server.

Build from the source

  1. clone this repo - git clone
  2. build the logger - cd dkll && docker build -t umputun/dkll .

alternatively use provided Makefile, i.e. make test lint docker


Server mode runs syslog server collecting records sent by dkll agent (see below). All records parsed, analyzed and stored in mongodb (capped collection). Optionally, records can be sent to <host>/<container>.log files as well as to merged dkll.log file. All files rotated and compressed automatically.


  1. copy provided compose-server.yml to docker-compose.yml
  2. adjust docker-compose.yml if needed.
  3. pull containers - docker-compose pull
  4. start server - docker-compose up -d

command line options and env params:

dkll [OPTIONS] server [server-OPTIONS]

Application Options:
      --dbg                              show debug info [$DEBUG]

Help Options:
  -h, --help                             Show this help message

[server command options]
      --api-port=                      rest server port (default: 8080) [$API_PORT]
      --syslog-port=                   syslog server port (default: 5514) [$SYSLOG_PORT]
      --mongo=                         mongo URL [$MONGO]
      --mongo-timeout=                 mongo timeout (default: 5s) [$MONGO_TIMEOUT]
      --mongo-size=                    max collection size (default: 10000000000) [$MONGO_SIZE]
      --mongo-docs=                    max docs in collection (default: 50000000) [$MONGO_DOCS]
      --backup=                        backup log files location [$BACK_LOG]
      --merged                         enable merged log file [$BACK_MRG]

      --limit.container.max-size=      max log size, in megabytes (default: 100) [$MAX_SIZE]
      --limit.container.max-backups=   max number of rotated files (default: 10) [$MAX_BACKUPS]
      --limit.container.max-age=       max age of rotated files, days (default: 30) [$MAX_AGE]

      --limit.merged.max-size=         max log size, in megabytes (default: 100) [$MAX_SIZE]
      --limit.merged.max-backups=      max number of rotated files (default: 10) [$MAX_BACKUPS]
      --limit.merged.max-age=          max age of rotated files, days (default: 30) [$MAX_AGE]
  • mongo URL specify the standard mongodb connection string with db and collection extra parameters, e.g. mongodb://localhost:27017/admin?db=dkll&collection=logs
  • if backup defined dkll server will make host/container.log files in backup directory
  • merged parameter produces a single dkll.log file with all received records.

Parameters can be set in command directive (see docker-compose.yml) or as environment vars.


Records format (response):

type LogEntry struct {
	ID        string    `json:"id"`         // record ID
	Host      string    `json:"host"`       // host name
	Container string    `json:"container"`  // container
	Pid       int       `json:"pid"`        // process id
	Msg       string    `json:"msg"`        // log message
	Ts        time.Time `json:"ts"`         // reported time 
	CreatedTs time.Time `json:"cts"`        // creation time
  • GET /v1/last - get last records LogEntry
  • POST /v1/find - find records for given Request
type Request struct {
	LastID     string    `json:"id"`                   // get records after this id
	Limit      int       `json:"max"`                  // max size of response, i.e. number of messages one request can return
	Hosts      []string  `json:"hosts,omitempty"`      // list of hosts, can be exact match or regex in from of /regex/
	Containers []string  `json:"containers,omitempty"` // list of containers, can be regex as well
	Excludes   []string  `json:"excludes,omitempty"`   // list of excluded containers, can be regex
	FromTS     time.Time `json:"from_ts,omitempty"`    
	ToTS       time.Time `json:"to_ts,omitempty"`
  • POST /v1/stream?timeout=10s - find records for given Request and stream it. Terminate stream on timeout inactivity.


DKLL server uses mongo db to save and access records. It is possible and almost trivial to replace mongo with different backend by implementing 2 interfaces (Publisher and DataService) with just 3 functions:

  • Publish(records []core.LogEntry) (err error)
  • LastPublished() (entry core.LogEntry, err error)
  • Find(req core.Request) ([]core.LogEntry, error)

Security and auth

Both syslog and http don't restrict access. To allow some basic auth the simplest way is to run dkll server behind nginx-le proxy with basic auth configured on nginx level. To limit access to syslog port (514) firewall (internal or external) cab be used.

TODO: example


Agent container runs on each host and collects logs from all containers on the host. The logs sent to remote dkll server and/or stored and rotated locally. The agent can intercept logs from containers configured with a logging driver that works with docker logs (journald and json-file).

To deploy agent use provided compose-agent.yml

dkll [OPTIONS] agent [agent-OPTIONS]

Application Options:
      --dbg                show debug info [$DEBUG]

Help Options:
  -h, --help               Show this help message

[agent command options]
      -d, --docker=        docker host (default: unix:///var/run/docker.sock) [$DOCKER_HOST]
          --syslog         enable logging to syslog [$LOG_SYSLOG]
          --syslog-host=   syslog host (default: [$SYSLOG_HOST]
          --syslog-prefix= syslog prefix (default: docker/) [$SYSLOG_PREFIX]
          --files          enable logging to files [$LOG_FILES]
          --max-size=      size of log triggering rotation (MB) (default: 10) [$MAX_SIZE]
          --max-files=     number of rotated files to retain (default: 5) [$MAX_FILES]
          --max-age=       maximum number of days to retain (default: 30) [$MAX_AGE]
          --mix-err        send error to std output log file [$MIX_ERR]
          --loc=           log files locations (default: logs) [$LOG_FILES_LOC]
      -x, --exclude=       excluded container names [$EXCLUDE]
      -i, --include=       included container names [$INCLUDE]
      -j, --json           wrap message with JSON envelope [$JSON]
          --demo           demo mode, generates simulated log entries [$DEMO]
          --demo-every=    demo interval (default: 3s) [$DEMO_EVERY]
  • at least one of destinations (files or syslog) should be allowed
  • location of log files can be mapped to host via volume, ex: - ./logs:/srv/logs (see compose-agent.yml)
  • both --exclude and --include flags are optional and mutually exclusive, i.e. if --exclude defined --include not allowed, and vise versa.

Demo mode

Defining --demo or $DEMO switches agent to demo mode emitting fake log messages from fake containers. Everything preconfigured in compose-demo.yml and can be activated with MONGO_PASSWD=<any random password> docker-compose -f compose-demo.yml up.


Command line client accessing dkll server and printing the content.


DKLL client should be used directly as a compiled binary. You can get precompiled release or build it from the source (make deploy).

dkll [OPTIONS] client [client-OPTIONS]

Application Options:
      --dbg       show debug info [$DEBUG]

Help Options:
  -h, --help      Show this help message

[client command options]
      -a, --api=  API endpoint (client) [$DKLL_API]
      -c=         show container(s) only
      -h=         show host(s) only
      -x=         exclude container(s)
      -m          show syslog timestamp
      -p          show pid
      -s          show syslog messages
      -f          follow mode
      -t          tail mode
      -n=         show N records
      -g=         grep on entire record
      -G=         un-grep on entire record
          --tail= number of initial records (default: 10)
          --tz=   time zone (default: Local)
  • containers (-c), hosts (-h) and exclusions (-x) can be repeated multiple times.
  • both containers and hosts support regex inside "/", i.e. /^something/


  • go v1.11 and above required
  • repository uses modules and should be cloned outside of GOPATH
  • dkll server tests need mongo up and running, i.e. docker run -d --name=mongo -p 27017:27017 mongo


Agent, server and client to collect and access logs in dockerized infrastructure







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