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Podman performance guide

The performance of Podman may be influenced by a number of factors, such as,

  • the specified Podman command-line options and configuration
  • the OCI runtime
  • the host file system
  • the container image

Changing any of these may or may not have any noticeable effect on the performance of Podman on your system.

Using a separate user account for benchmarking

Some performance tips, such as using a different storage driver would require the user to run podman system reset, which erases all containers and container images for the user. Instead of benchmarking different alternatives in your own home directory, you could create a new user that afterwards can be removed.

Example: Specify the storage driver vfs and run /bin/true in an Alpine container

Interactively

sudo useradd testuser
sudo machinectl shell testuser@
podman pull docker.io/library/alpine
/usr/bin/time -v podman --storage-driver=vfs run --rm docker.io/library/alpine /bin/true
exit

Noninteractively

sudo useradd testuser
systemd-run --machine=testuser@ --quiet --user --collect --pipe --wait \
   podman --storage-driver=vfs pull docker.io/library/alpine
systemd-run --machine=testuser@ --quiet --user --collect --pipe --wait \
   /usr/bin/time -v podman --storage-driver=vfs run --rm docker.io/library/alpine /bin/true

The command /usr/bin/time -v measures and displays benchmarking information.

Performance considerations

Use a fast OCI runtime

Podman uses an OCI runtime when running containers. The fastest OCI runtime is probably crun.

Check that you are using crun

$ podman info --format={{.Host.OCIRuntime.Name}}
crun

To benchmark an OCI runtime, create a test user account and specify the OCI runtime path with --runtime.

Choosing a storage driver

The following storage drivers are listed from fastest to slowest:

  1. native overlayfs
  2. fuse-overlayfs
  3. vfs

There is one notable exception to this speed ranking. Creating a container takes significantly longer with native overlayfs than fuse-overlayfs when these conditions are all met:

  • rootless Podman is used
  • a modified UID/GID mapping is used
  • native overlayfs is used
  • no container has yet been created with the specified container image and UID/GID mapping

Runtime speed is not affected. Only podman create and the container creation phases of podman run and podman build are affected. For more details, see GitHub comment. Command-line options that modify the UID/GID mapping are for example --userns, --uidmap and --gidmap. The command-line option --userns auto is particularly affected by this performance penalty, because different UID/GID mappings could potentially be used on each invocation. For other uses of --userns, --uidmap and --gidmap the performance penalty is a one-time cost that only occurs the first time the command is run.

Using native overlayfs as an unprivileged user is only available for Podman version >= 3.1 on a Linux kernel version >= 5.12.

To show the current storage driver

$ podman info -f {{.Store.GraphDriverName}}
overlay
$ podman info -f '{{index .Store.GraphStatus "Native Overlay Diff"}}'
true
Storage driver Result of podman info -f {{.Store.GraphDriverName}} Result of podman info -f '{{index .Store.GraphStatus "Native Overlay Diff"}}
native overlayfs overlay true
fuse-overlayfs overlay false
VFS vfs false

Before changing the storage driver, running podman system reset is required. The command erases all containers and container images for the user. See the example above "Using a separate user account for benchmarking" for how to benchmark a storage driver in a separate test account.

Specifying the storage driver with command-line options

Storage driver Podman command
native overlayfs podman --storage-driver=overlay run ...
fuse-overlayfs podman --storage-driver=overlay --storage-opt overlay.mount_program=/usr/bin/fuse-overlayfs run ...
VFS podman --storage-driver=vfs run ...

Configuring the default storage driver

The default storage driver can be configured in /etc/containers/storage.conf and overridden by a user in ~/.config/containers/storage.conf

To configure native overlayfs:

[storage]
driver = "overlay"

To configure fuse-overlayfs:

[storage]
driver = "overlay"
[storage.options.overlay]
mount_program = "/usr/bin/fuse-overlayfs"

To configure VFS:

[storage]
driver = "vfs"

See storage.conf(5) for all available configuration settings.

Network performance for rootless Podman

When using rootless Podman, network traffic is normally passed through slirp4netns. This comes with a performance penalty.

You can avoid using slirp4netns in the following ways:

  • Use socket activation for listening network sockets. Communication over the activated socket does not pass through slirp4netns, so it has the same performance characteristics as the normal network on the host. Socket-activated services can be started and stopped in different ways:

    • Let systemd start the service when the first client connects. Let the service terminate by itself after some time of inactivity. Using a service on demand, can free up compute resources.
    • Start the service explicitly (systemctl --user enable foobar.service). If the service is already running when the first client connects, there will be no delay due to container startup. The socket activation tutorial provides more information about socket activation support in Podman.

  • Use the network driver pasta. Pasta is under development and currently needs a patched Podman to run.

  • Set up the network manually as root. Create a bridge and virtual ethernet pair (VETH). See the example posted on the Podman mailing list. See also the section DIY networking in Podman-Rootless-Networking.pdf.

  • Use --network=host. No network namespace is created. The container will use the host’s network. Note: By using --network=host, the container is given full access to local system services such as D-bus and is therefore considered insecure.

Lazy pulling of container images

Podman supports lazy pulling for the following container image formats:

  • zstd:chunked

  • eStargz

zstd:chunked has better performance than eStargz.

See the article Pull container images faster with partial pulls by Giuseppe Scrivano and Dan Walsh.

Choosing a host file system

Lazy pulling of container images can run more efficiently when the file system has reflink support. The file systems XFS and BTRFS have reflink support.

Option --log-driver

The podman run option --log-driver specifies the logging driver for the container.

If logging is not needed, consider using --log-driver=none to disable logging.

Reuse the package repository cache when building container images

The first step of a container build is often to download metadata from the package repositories and post-process that data.

To speed up container builds, you could prepare a directory on the host that contains the package metadata and then make the directory available to the container build by using an overlay mount.

Example : Speed up podman build by reusing the DNF metadata cache

In this example the containers are based on Fedora 36.

First create an empty directory on the host, for example $HOME/dnf_cache_f36.

$ mkdir $HOME/dnf_cache_f36

Fill the directory with the most recent dnf metadata cache.

$ podman run --rm -v $HOME/dnf_cache_f36:/var/cache/dnf:Z registry.fedoraproject.org/fedora:36 dnf makecache

Create a new directory, for example, $HOME/ctr and a file $HOME/ctr/Containerfile with these contents

FROM registry.fedoraproject.org/fedora:36
RUN dnf -y update && dnf -y install cowsay && dnf clean all

To build the Containerfile using the prepared metadata cache, provide the directory $HOME/dnf_cache_f36 as an overlay mount (volume option :O)

$ podman build -v $HOME/dnf_cache_f36:/var/cache/dnf:O -t cowsay $HOME/ctr

The article Speeding up container image builds with Buildah by Dan Walsh provides more details.