how to find MAX memory from docker stats?

Question

With docker stats you can see the memory usage of a container over time.

Is there a way to find what the highest value of memory usage was while running docker stats?

Answer 1

I took a sampling script from here and aggregated data by @pl_rock. But be careful - the sort command only compares string values - so the results are usually wrong (but ok for me). Also mind that docker is sometimes reporting wrong numbers (ie. more allocated mem than physical RAM).

Here is the script:

#!/bin/bash  "$@" & # Run the given command line in the background. pid=$!  echo "" > stats  while true; do   sleep 1   sample="$(ps -o rss= $pid 2> /dev/null)" || break    docker stats --no-stream --format "{{.MemUsage}} {{.Name}} {{.Container}}" | awk '{ print strftime("%Y-%m-%d %H:%M:%S"), $0 }' >> stats done  for containerid in `awk '/.+/ { print $7 }' stats | sort | uniq` do     grep "$containerid" stats | sort -r -k3 | tail -n 1     # maybe: | sort -r -k3 -h | head -n 1     # see comment below (didnt tested) done 

Answer 2

If you need to find the peak usage you are better off requesting the .MemPerc option and calculating based on the total memory (unless you restricted the memory available to the container). .MemUsage has units which change during the life of the container which mess with the result.

docker stats --format 'CPU: {{.CPUPerc}}\tMEM: {{.MemPerc}}'

You can stream an ongoing log to a file (or script).

To get just the max memory as originally requested:

(timeout 120 docker stats --format '{{.MemPerc}}' <CONTAINER_ID> \
  | sed 's/\x1b\[[0-9;]*[a-zA-Z]//g' ; echo) \
  | tr -d '%' | sort -k1,1n | tail -n 1

And then you can ask the system for its total RAM (again assuming you didn't limit the RAM available to docker) and calculate:

awk '/MemTotal/ {print $2}' /proc/meminfo

You would need to know how long the container is going to run when using timeout as above, but if docker stats was run without this in background submitted by a script it could kill it once the container completed.

...

This command allows you to generate a time-series of the cpu/memory load:

(timeout 20 docker stats --format \
  'CPU: {{.CPUPerc}}\tMEM: {{.MemPerc}}' <CONTAINER_ID> \
  | sed 's/\x1b\[[0-9;]*[a-zA-Z]//g' ; echo) \
  | gzip -c > monitor.log.gz

Note that it pipes into gzip. In this form you get ~2 rows per second so the file would get large rapidly if you don't.

I'd advise this for benchmarking and trouble shooting rather than use on production containers