Docker log sharing

View logs for a container or service

1. the docker service logs command shows information logged by all containers participating in a service. The information that is logged and the format of the log depends almost entirely on the container’s endpoint command.( this is for docker swarm)
2. [By default], docker logs or docker service logs shows the command’s output just as it would appear if you ran the command interactively in a terminal. UNIX and Linux commands typically open three I/O streams when they run, called STDIN, STDOUT, and STDERR. STDIN is the commmand’s input stream, which may include input from the keyboard or input from another command. STDOUT is usually a command’s normal output, and STDERR is typically used to output error messages. By default, docker logs shows the command’s STDOUT and STDERR.

Configure logging drivers

Each Docker daemon has a default logging driver, which each container uses unless you configure it to use a different logging driver.

Configure the default logging driver

To configure the Docker daemon to default to a specific logging driver, set the value of log-driver to the name of the logging driver in the daemon.json file, which is located in /etc/docker/ on Linux hosts.
The default logging driver is json-file. The following example explicitly sets the default logging driver to syslog:

{  "log-driver": "syslog"}

If the logging driver has configurable options, you can set them in the daemon.json file as a JSON array with the key log-opts. The following example sets two configurable options on the json-file logging driver:

{  "log-driver": "json-file",  "log-opts": {    "labels": "production_status",    "env": "os,customer"  }}

Configure the logging driver for a container

When you start a container, you can configure it to use a different logging driver than the Docker daemon’s default, using the –log-driver** flag. If the logging driver has configurable options, you can set them using one or more instances of the –log-opt = flag. Even if the container uses the default logging driver, it can use different configurable options.**

The following example starts an Alpine container with the none logging driver.

$ docker run -it --log-driver none alpine ash

To find the current logging driver for a running container, if the daemon is using the json-file logging driver, run the following docker inspect command, substituting the container name or ID for < container>:

$ docker inspect -f '{{.HostConfig.LogConfig.Type}}' <CONTAINER>json-file

Use a logging driver plugin

Docker logging plugins allow you to extend and customize Docker’s logging capabilities beyond those of the built-in logging drivers. A logging service provider can implement their own plugins and make them available on Docker Hub, Docker Store, or a private registry. This topic shows how a user of that logging service can configure Docker to use the plugin.

Configure a container to use the plugin as the logging driver

After the plugin is installed, you can configure a container to use the plugin as its logging driver by specifying the –log-driver flag to docker run, as detailed in the logging overview. If the logging driver supports additional options, you can specify them using one or more –log-opt flags with the option name as the key and the option value as the value.

Install the logging driver plugin

To install a logging driver plugin, use docker plugin install < org/image>, using the information provided by the plugin developer.
You can list all installed plugins using docker plugin ls, and you can inspect a specific plugin using docker inspect.

Log tags for logging driver

The tag log option specifies how to format a tag that identifies the container’s log messages. By default, the system uses the first 12 characters of the container ID. To override this behavior, specify a tag option:

$ docker run --log-driver=fluentd --log-opt fluentd-address=myhost.local:24224 --log-opt tag="mailer"

Docker supports some special template markup you can use when specifying a tag’s value:

Markup Description {{.ID}} The first 12 characters of the container ID. {{.FullID}} The full container ID. {{.Name}} The container name. {{.ImageID}} The first 12 characters of the container’s image ID. {{.ImageFullID}} The container’s full image ID. {{.ImageName}} The name of the image used by the container. {{.DaemonName}} The name of the docker program (docker).

---

For example, specifying a –log-opt tag=”{{.ImageName}}/{{.Name}}/{{.ID}}” value yields syslog log lines like:

Aug  7 18:33:19 HOSTNAME hello-world/foobar/5790672ab6a0[9103]: Hello from Docker.

At startup time, the system sets the container_name field and {{.Name}} in the tags. If you use docker rename to rename a container, the new name is not reflected in the log messages. Instead, these messages continue to use the original container name.

available log driver

C:\Users\mcong\Desktop\github\docker-ce\components\engine\daemon\logdrivers_linux.go

import (    // Importing packages here only to make sure their init gets called and    // therefore they register themselves to the logdriver factory.    _ "github.com/docker/docker/daemon/logger/awslogs"    _ "github.com/docker/docker/daemon/logger/fluentd"    _ "github.com/docker/docker/daemon/logger/gcplogs"    _ "github.com/docker/docker/daemon/logger/gelf"    _ "github.com/docker/docker/daemon/logger/journald"    _ "github.com/docker/docker/daemon/logger/jsonfilelog"    _ "github.com/docker/docker/daemon/logger/logentries"    _ "github.com/docker/docker/daemon/logger/splunk"    _ "github.com/docker/docker/daemon/logger/syslog")