semaphoreci: caching and more robust creation of container image

lxc-create in semaphore sometimes fails with

    ERROR: Unable to fetch GPG key from keyserver

Which often happens behind proxies. As the default key server is a load
balancer, retry a few times.

Also, cache the container image between runs, and only recreate it when
it is older than a week.

1 files changed, 37 insertions, 20 deletions

diff --git a/semaphoreci/setup.sh b/semaphoreci/setup.sh
index b8cdba8033..c904a300a1 100755
--- a/semaphoreci/setup.sh
+++ b/semaphoreci/setup.sh
@@ -7,6 +7,36 @@ DISTRO=${DISTRO:-debian}
 RELEASE=${RELEASE:-buster}
 ARCH=${ARCH:-amd64}
 CONTAINER=${RELEASE}-${ARCH}
+MAX_CACHE_AGE=604800  # one week
+CACHE=${SEMAPHORE_CACHE_DIR:=/tmp}/${CONTAINER}.img.tar.gz
+
+create_container() {
+    # create autopkgtest LXC image; this sometimes fails with "Unable to fetch
+    # GPG key from keyserver", so retry a few times
+    for retry in $(seq 5); do
+        sudo lxc-create -n $CONTAINER -t download -- -d $DISTRO -r $RELEASE -a $ARCH && break
+        sleep $((retry*retry))
+    done
+
+    # unconfine the container, otherwise some tests fail
+    echo 'lxc.apparmor.profile = unconfined' | sudo tee -a /var/lib/lxc/$CONTAINER/config
+
+    sudo lxc-start -n $CONTAINER
+
+    # enable source repositories so that apt-get build-dep works
+    sudo lxc-attach -n $CONTAINER -- sh -ex <<EOF
+sed 's/^deb/deb-src/' /etc/apt/sources.list >> /etc/apt/sources.list.d/sources.list
+# wait until online
+while [ -z "\$(ip route list 0/0)" ]; do sleep 1; done
+apt-get -q update
+apt-get -y dist-upgrade
+apt-get install -y eatmydata
+EOF
+    sudo lxc-stop -n $CONTAINER
+
+    # cache it
+    sudo tar cpzf "$CACHE" /var/lib/lxc/$CONTAINER
+}
 
 # remove semaphore repos, some of them don't work and cause error messages
 sudo rm -f /etc/apt/sources.list.d/*
@@ -17,25 +47,12 @@ sudo apt-get -q update
 sudo apt-get install -y -t xenial-backports lxc
 sudo apt-get install -y python3-debian git dpkg-dev fakeroot
 
-AUTOPKGTESTDIR=${SEMAPHORE_CACHE_DIR:-/tmp}/autopkgtest
+AUTOPKGTESTDIR=$SEMAPHORE_CACHE_DIR/autopkgtest
 [ -d $AUTOPKGTESTDIR ] || git clone --quiet --depth=1 https://salsa.debian.org/ci-team/autopkgtest.git "$AUTOPKGTESTDIR"
 
-# TODO: cache container image (though downloading/building it takes < 1 min)
-# create autopkgtest LXC image
-sudo lxc-create -n $CONTAINER -t download -- -d $DISTRO -r $RELEASE -a $ARCH
-
-# unconfine the container, otherwise some tests fail
-echo 'lxc.apparmor.profile = unconfined' | sudo tee -a /var/lib/lxc/$CONTAINER/config
-
-sudo lxc-start -n $CONTAINER
-
-# enable source repositories so that apt-get build-dep works
-sudo lxc-attach -n $CONTAINER -- sh -ex <<EOF
-sed 's/^deb/deb-src/' /etc/apt/sources.list >> /etc/apt/sources.list.d/sources.list
-# wait until online
-while [ -z "\$(ip route list 0/0)" ]; do sleep 1; done
-apt-get -q update
-apt-get -y dist-upgrade
-apt-get install -y eatmydata
-EOF
-sudo lxc-stop -n $CONTAINER
+# use cached container image, unless older than a week
+if [ -e "$CACHE" ] && [ $(( $(date +%s) - $(stat -c %Y "$CACHE") )) -le $MAX_CACHE_AGE ]; then
+    sudo tar -C / -xpzf "$CACHE"
+else
+    create_container
+fi