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Add pkg/logwrite which writes and rotates log files

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This process connects to memlogd and streams logs to individual files,
one per log. It keeps track of how many bytes have been written to each
file and rotates when the file size exceeds a defined threshold.

By default the maximum size of each file before rotation is 1MiB and
we keep up to 10 files per log.

Signed-off-by: David Scott <dave.scott@docker.com>
This commit is contained in:
David Scott
2018-07-02 15:41:37 +01:00
parent 4b4d56913d
commit 565f787bb3
8 changed files with 323 additions and 24 deletions
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50
docs/logging.md
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@@ -39,8 +39,8 @@ The circular buffer has a fixed size (overridden by the command-line argument
To store the logs somewhere more permanent, for example a disk or a remote
network service, a service should be added to the yaml which connects to
`memlogd` and streams the logs. The example program `logread` in the `memlogd`
package demonstrates how to do this.
`memlogd` and streams the logs. The `logwrite` service described below shows
how to do this.
### Message format
@@ -52,33 +52,35 @@ where `<timestamp>` is an RFC3339-formatted timestamp, `<log>` is the name of
the log (e.g. `docker-ce.out`) and `<body>` is the output. The `<log>` must
not contain the character `;`.
### Usage examples
## logwrite: writing logs to disk
The service `pkg/logwrite` connects to `memlogd` and streams the logs to files
in `/var/log`. The logs are automatically rotated; by default each file has
a maximum size of 1 MiB and up to 10 files are kept per log. The arguments
`-max-log-files` and `-max-log-size` can be used to override these defaults.
Here is an example log file:
```
/ # logread -f
2018-07-05T13:22:32Z,memlogd;memlogd started
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;eth0: waiting for carrier
2018-07-05T13:22:32Z,onboot.001-dhcpcd.err;eth0: could not detect a useable init
system
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;eth0: carrier acquired
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;DUID 00:01:00:01:22:d0:d8:18:02:50:00:00:00:02
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;eth0: IAID 00:00:00:02
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;eth0: adding address fe80::d33a:3936:
2ee4:5c8c
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;eth0: soliciting an IPv6 router
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;eth0: soliciting a DHCP lease
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;eth0: offered 192.168.65.4 from 192.1
68.65.1 `vpnkit'
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;eth0: leased 192.168.65.4 for 7200 se
# cat /var/log/onboot.001-dhcpcd.out
2018-07-08T09:16:53Z onboot.001-dhcpcd.out eth0: waiting for carrier
2018-07-08T09:16:53Z onboot.001-dhcpcd.out eth0: carrier acquired
2018-07-08T09:16:53Z onboot.001-dhcpcd.out DUID 00:01:00:01:22:d4:93:05:02:50:00
:00:00:06
2018-07-08T09:16:53Z onboot.001-dhcpcd.out eth0: IAID 00:00:00:06
2018-07-08T09:16:53Z onboot.001-dhcpcd.out eth0: adding address fe80::f346:56a6:590d:5ea4
2018-07-08T09:16:53Z onboot.001-dhcpcd.out eth0: soliciting an IPv6 router
2018-07-08T09:16:53Z onboot.001-dhcpcd.out eth0: soliciting a DHCP lease
2018-07-08T09:16:53Z onboot.001-dhcpcd.out eth0: offered 192.168.65.8 from 192.168.65.1 `vpnkit'
2018-07-08T09:16:53Z onboot.001-dhcpcd.out eth0: leased 192.168.65.8 for 7200 se
conds
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;eth0: adding route to 192.168.65.0/24
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;eth0: adding default route via 192.16
2018-07-08T09:16:53Z onboot.001-dhcpcd.out eth0: adding route to 192.168.65.0/24
2018-07-08T09:16:53Z onboot.001-dhcpcd.out eth0: adding default route via 192.16
8.65.1
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;exiting due to oneshot
2018-07-05T13:22:32Z,onboot.001-dhcpcd.out;dhcpcd exited
^C
2018-07-08T09:16:53Z onboot.001-dhcpcd.out exiting due to oneshot
2018-07-08T09:16:53Z onboot.001-dhcpcd.out dhcpcd exited
```
Current issues and limitations:
## Current issues and limitations:
- No docker logger plugin support yet - it could be nice to add support to
memlogd, so the docker container logs would also be gathered in one place