mirror of https://github.com/docker/docs.git
121 lines
4.4 KiB
Markdown
121 lines
4.4 KiB
Markdown
---
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description: Learn how to read container logs locally when using a third party logging solution.
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keywords: docker, logging, driver
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title: Use docker logs to read container logs for remote logging drivers
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---
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## Overview
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Prior to Docker Engine 20.10, the [`docker logs` command](../../../engine/reference/commandline/logs.md)
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could only be used with logging drivers that supported for containers using the
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`local`, `json-file`, or `journald` log drivers. However, many third party logging
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drivers had no support for locally reading logs using `docker logs`
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This created multiple problems when attempting to gather log data in an
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automated and standard way. Log information could only be accessed and viewed
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through the third-party solution in the format specified by that
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third-party tool.
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Starting with Docker Engine 20.10, you can use `docker logs` to read container
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logs regardless of the configured logging driver or plugin. This capability,
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referred to as "dual logging", allows you to use `docker logs` to read container
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logs locally in a consistent format, regardless of the log driver used, because
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the engine is configured to log information to the “local” logging driver. Refer
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to [Configure the default logging driver](/config/containers/logging/configure)
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for additional information.
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## Prerequisites
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No configuration changes are needed to use dual logging. Docker Engine 20.10 and
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up automatically enable dual logging if the configured logging driver does not
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support reading logs.
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The following examples show the result of running a `docker logs` command with
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and without dual logging availability:
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### Without dual logging capability:
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When a container or `dockerd` was configured with a remote logging driver such
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as `splunk`, an error was displayed when attempting to read container logs
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locally:
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- Step 1: Configure Docker daemon
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```console
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$ cat /etc/docker/daemon.json
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{
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"log-driver": "splunk",
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"log-opts": {
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...
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}
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}
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```
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- Step 2: Start the container
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```console
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$ docker run -d busybox --name testlog top
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```
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- Step 3: Read the container logs
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```console
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$ docker logs 7d6ac83a89a0
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Error response from daemon: configured logging driver does not support reading
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```
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### With dual logging capability:
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To configure a container or docker with a remote logging driver such as splunk:
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- Step 1: Configure Docker daemon
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```console
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$ cat /etc/docker/daemon.json
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{
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"log-driver": "splunk",
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"log-opts": {
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...
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}
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}
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```
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- Step 2: Start the container
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```console
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$ docker run -d busybox --name testlog top
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```
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- Step 3: Read the container logs
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```console
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$ docker logs 7d6ac83a89a0
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2019-02-04T19:48:15.423Z [INFO] core: marked as sealed
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2019-02-04T19:48:15.423Z [INFO] core: pre-seal teardown starting
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2019-02-04T19:48:15.423Z [INFO] core: stopping cluster listeners
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2019-02-04T19:48:15.423Z [INFO] core: shutting down forwarding rpc listeners
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2019-02-04T19:48:15.423Z [INFO] core: forwarding rpc listeners stopped
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2019-02-04T19:48:15.599Z [INFO] core: rpc listeners successfully shut down
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2019-02-04T19:48:15.599Z [INFO] core: cluster listeners successfully shut down
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```
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> **Note**
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>
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> For a local driver, such as `json-file` and `journald`, there is no difference in
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> functionality before or after the dual logging capability became available.
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> The log is locally visible in both scenarios.
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## Limitations
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- You cannot specify more than one log driver.
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- If a container using a logging driver or plugin that sends logs remotely
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suddenly has a "network" issue, no ‘write’ to the local cache occurs.
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- If a write to `logdriver` fails for any reason (file system full, write
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permissions removed), the cache write fails and is logged in the daemon log.
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The log entry to the cache is not retried.
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- Some logs might be lost from the cache in the default configuration because a
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ring buffer is used to prevent blocking the stdio of the container in case of
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slow file writes. An admin must repair these while the daemon is shut down.
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