Docker apps logging with Filebeat and Logstash - docker

Question

I have a set of dockerized applications scattered across multiple servers and trying to setup production-level centralized logging with ELK. I'm ok with the ELK part itself, but I'm a little confused about how to forward the logs to my logstashes.
I'm trying to use Filebeat, because of its loadbalance feature.
I'd also like to avoid packing Filebeat (or anything else) into all my dockers, and keep it separated, dockerized or not.
How can I proceed?
I've been trying the following. My Dockers log on stdout so with a non-dockerized Filebeat configured to read from stdin I do:
docker logs -f mycontainer | ./filebeat -e -c filebeat.yml
That appears to work at the beginning. The first logs are forwarded to my logstash. The cached one I guess. But at some point it gets stuck and keep sending the same event
Is that just a bug or am I headed in the wrong direction? What solution have you setup?

Answer 1

Here's one way to forward docker logs to the ELK stack (requires docker >= 1.8 for the gelf log driver):
Start a Logstash container with the gelf input plugin to reads from gelf and outputs to an Elasticsearch host (ES_HOST:port):
docker run --rm -p 12201:12201/udp logstash \
logstash -e 'input { gelf { } } output { elasticsearch { hosts => ["ES_HOST:PORT"] } }'
Now start a Docker container and use the gelf Docker logging driver. Here's a dumb example:
docker run --log-driver=gelf --log-opt gelf-address=udp://localhost:12201 busybox \
/bin/sh -c 'while true; do echo "Hello $(date)"; sleep 1; done'
Load up Kibana and things that would've landed in docker logs are now visible. The gelf source code shows that some handy fields are generated for you (hat-tip: Christophe Labouisse): _container_id, _container_name, _image_id, _image_name, _command, _tag, _created.
If you use docker-compose (make sure to use docker-compose >= 1.5) and add the appropriate settings in docker-compose.yml after starting the logstash container:
log_driver: "gelf"
log_opt:
gelf-address: "udp://localhost:12201"

Answer 2

Docker allows you to specify the logDriver in use. This answer does not care about Filebeat or load balancing.
In a presentation I used syslog to forward the logs to a Logstash (ELK) instance listening on port 5000.
The following command constantly sends messages through syslog to Logstash:
docker run -t -d --log-driver=syslog --log-opt syslog-address=tcp://127.0.0.1:5000 ubuntu /bin/bash -c 'while true; do echo "Hello $(date)"; sleep 1; done'

Answer 3

Using filebeat you can just pipe docker logs output as you've described. Behavior you are seeing definitely sounds like a bug, but can also be the partial line read configuration hitting you (resend partial lines until newline symbol is found).
A problem I see with piping is possible back pressure in case no logstash is available. If filebeat can not send any events, it will buffer up events internally and at some point stop reading from stdin. No idea how/if docker protects from stdout becoming unresponsive. Another problem with piping might be restart behavior of filebeat + docker if you are using docker-compose. docker-compose by default reuses images + image state. So when you restart, you will ship all old logs again (given the underlying log file has not been rotated yet).
Instead of piping you can try to read the log files written by docker to the host system. The default docker log driver is the json log driver . You can and should configure the json log driver to do log-rotation + keep some old files (for buffering up on disk). See max-size and max-file options. The json driver puts one line of 'json' data for every line to be logged. On the docker host system the log files are written to /var/lib/docker/containers/container_id/container_id-json.log . These files will be forwarded by filebeat to logstash. If logstash or network becomes unavailable or filebeat is restarted, it continues forwarding log lines where it left of (given files have been not deleted due to log rotation). No events will be lost. In logstash you can use the json_lines codec or filter to parse the json lines and a grok filter to gain some more information from your logs.
There has been some discussion about using libbeat (used by filebeat for shipping log files) to add a new log driver to docker. Maybe it is possible to collect logs via dockerbeat in the future by using the docker logs api (I'm not aware of any plans about utilising the logs api, though).
Using syslog is also an option. Maybe you can get some syslog relay on your docker host load balancing log events. Or have syslog write log files and use filebeat to forward them. I think rsyslog has at least some failover mode. You can use logstash syslog input plugin and rsyslog to forward logs to logstash with failover support in case the active logstash instance becomes unavailable.

Answer 4

I created my own docker image using the Docker API to collect the logs of the containers running on the machine and ship them to Logstash thanks to Filebeat. No need to install or configure anything on the host.
Check it out and tell me if it suits your needs: https://hub.docker.com/r/bargenson/filebeat/.
The code is available here: https://github.com/bargenson/docker-filebeat

Answer 5

Just for helping others that need to do this, you can simply use Filebeat to ship the logs. I would use the container by #brice-argenson, but I needed SSL support so I went with a locally installed Filebeat instance.
The prospector from filebeat is (repeat for more containers):
- input_type: log
paths:
- /var/lib/docker/containers/<guid>/*.log
document_type: docker_log
fields:
dockercontainer: container_name
It sucks a bit that you need to know the GUIDs as they could change on updates.
On the logstash server, setup the usual filebeat input source for logstash, and use a filter like this:
filter {
if [type] == "docker_log" {
json {
source => "message"
add_field => [ "received_at", "%{#timestamp}" ]
add_field => [ "received_from", "%{host}" ]
}
mutate {
rename => { "log" => "message" }
}
date {
match => [ "time", "ISO8601" ]
}
}
}
This will parse the JSON from the Docker logs, and set the timestamp to the one reported by Docker.
If you are reading logs from the nginx Docker image, you can add this filter as well:
filter {
if [fields][dockercontainer] == "nginx" {
grok {
match => { "message" => "(?m)%{IPORHOST:targethost} %{COMBINEDAPACHELOG}" }
}
mutate {
convert => { "[bytes]" => "integer" }
convert => { "[response]" => "integer" }
}
mutate {
rename => { "bytes" => "http_streamlen" }
rename => { "response" => "http_statuscode" }
}
}
}
The convert/renames are optional, but fixes an oversight in the COMBINEDAPACHELOG expression where it does not cast these values to integers, making them unavailable for aggregation in Kibana.

Answer 6

I verified what erewok wrote above in a comment:
According to the docs, you should be able to use a pattern like this
in your prospectors.paths: /var/lib/docker/containers/*/*.log – erewok
Apr 18 at 21:03
The docker container guids, represented as the first '*', are correctly resolved when filebeat starts up. I do not know what happens as containers are added.