1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
|
#!/bin/sh
# vim: set ts=4 et:
set -eu
DEVICE=/dev/xvdf
TARGET=/mnt/target
# what bootloader should we use?
[ -d "/sys/firmware/efi" ] && BOOTLOADER=grub-efi || BOOTLOADER=syslinux
die() {
printf '\033[1;31mERROR:\033[0m %s\n' "$@" >&2 # bold red
exit 1
}
einfo() {
printf '\n\033[1;36m> %s\033[0m\n' "$@" >&2 # bold cyan
}
rc_add() {
runlevel="$1"; shift # runlevel name
services="$*" # names of services
for svc in $services; do
mkdir -p "$TARGET/etc/runlevels/$runlevel"
ln -s "/etc/init.d/$svc" "$TARGET/etc/runlevels/$runlevel/$svc"
echo " * service $svc added to runlevel $runlevel"
done
}
wgets() (
url="$1" # url to fetch
sha256="$2" # expected SHA256 sum of output
dest="$3" # output path and filename
wget -T 10 -q -O "$dest" "$url"
echo "$sha256 $dest" | sha256sum -c > /dev/null
)
validate_block_device() {
lsblk -P --fs "$DEVICE" >/dev/null 2>&1 || \
die "'$DEVICE' is not a valid block device"
if lsblk -P --fs "$DEVICE" | grep -vq 'FSTYPE=""'; then
die "Block device '$DEVICE' is not blank"
fi
}
fetch_apk_tools() {
store="$(mktemp -d)"
tarball="$(basename "$APK_TOOLS")"
wgets "$APK_TOOLS" "$APK_TOOLS_SHA256" "$store/$tarball"
tar -C "$store" -xf "$store/$tarball"
find "$store" -name apk
}
# mostly from Alpine's /sbin/setup-disk
setup_partitions() {
start=2M # Needed to align EBS partitions
line=
# create new partitions
(
for line in "$@"; do
case "$line" in
0M*) ;;
*) echo "$start,$line"; start= ;;
esac
done
) | sfdisk --quiet --label gpt "$DEVICE"
# we assume that the build host will create the new devices within 5s
tries=5
while [ ! -e "${DEVICE}1" ]; do
[ $tries -eq 0 ] && break
sleep 1
tries=$(( tries - 1 ))
done
[ -e "${DEVICE}1" ] || die "Expected new device ${DEVICE}1 not created"
}
make_filesystem() {
root_dev="$DEVICE"
if [ "$BOOTLOADER" = 'grub-efi' ]; then
# create a small EFI partition (remainder for root), and mount it
setup_partitions '5M,U,*' ',L'
root_dev="${DEVICE}2"
mkfs.vfat -n EFI "${DEVICE}1"
fi
mkfs.ext4 -O ^64bit -L / "$root_dev"
mount "$root_dev" "$TARGET"
if [ "$BOOTLOADER" = 'grub-efi' ]; then
mkdir -p "$TARGET/boot/efi"
mount -t vfat "${DEVICE}1" "$TARGET/boot/efi"
fi
}
setup_repositories() {
mkdir -p "$TARGET/etc/apk/keys"
echo "$REPOS" > "$TARGET/etc/apk/repositories"
}
fetch_keys() {
tmp="$(mktemp -d)"
wgets "$ALPINE_KEYS" "$ALPINE_KEYS_SHA256" "$tmp/alpine-keys.apk"
tar -C "$TARGET" --warning=no-unknown-keyword -xvf "$tmp/alpine-keys.apk" etc/apk/keys
rm -rf "$tmp"
}
install_base() {
$apk add --root "$TARGET" --no-cache --initdb alpine-base
# verify release matches
if [ "$VERSION" != "edge" ]; then
ALPINE_RELEASE=$(cat "$TARGET/etc/alpine-release")
[ "$RELEASE" = "$ALPINE_RELEASE" ] || \
die "Newer Alpine release detected: $ALPINE_RELEASE"
fi
}
setup_chroot() {
mount -t proc none "$TARGET/proc"
mount --bind /dev "$TARGET/dev"
mount --bind /sys "$TARGET/sys"
# Needed for bootstrap, will be removed in the cleanup stage.
install -Dm644 /etc/resolv.conf "$TARGET/etc/resolv.conf"
}
install_core_packages() {
chroot "$TARGET" apk --no-cache add $PKGS
chroot "$TARGET" apk --no-cache add --no-scripts $BOOTLOADER
# Disable starting getty for physical ttys because they're all inaccessible
# anyhow. With this configuration boot messages will still display in the
# EC2 console.
sed -Ei '/^tty[0-9]/s/^/#/' "$TARGET/etc/inittab"
# Enable the getty for the serial terminal. This will show the login prompt
# in the get-console-output API that's accessible by the CLI and the web
# console.
sed -Ei '/^#ttyS0:/s/^#//' "$TARGET/etc/inittab"
# Make it a little more obvious who is logged in by adding username to the
# prompt
sed -i "s/^export PS1='/&\\\\u@/" "$TARGET/etc/profile"
}
setup_mdev() {
cp /tmp/setup-ami.d/nvme-ebs-links "$TARGET/lib/mdev"
# insert nvme ebs mdev configs just above "# fallback" comment
sed -n -i \
-e '/# fallback/i \\n# ebs nvme links\nnvme[0-9]+n[0-9]+.* root:root 0660 */lib/mdev/nvme-ebs-links' \
-e 1x -e '2,${x;p}' -e '${x;p}' \
"$TARGET/etc/mdev.conf"
}
create_initfs() {
sed -Ei "s/^features=\"([^\"]+)\"/features=\"\1 $INITFS_FEATURES\"/" \
"$TARGET/etc/mkinitfs/mkinitfs.conf"
chroot "$TARGET" /sbin/mkinitfs $(basename $(find "$TARGET/lib/modules/"* -maxdepth 0))
}
install_bootloader() {
case "$BOOTLOADER" in
syslinux) install_extlinux ;;
grub-efi) install_grub_efi ;;
*) die "unknown bootloader '$BOOTLOADER'" ;;
esac
}
install_extlinux() {
# Must use disk labels instead of UUID or devices paths so that this works
# across instance familes. UUID works for many instances but breaks on the
# NVME ones because EBS volumes are hidden behind NVME devices.
#
# Enable ext4 because the root device is formatted ext4
#
# Shorten timeout (1/10s) as EC2 has no way to interact with instance console
#
# ttyS0 is the target for EC2s "Get System Log" feature whereas tty0 is the
# target for EC2s "Get Instance Screenshot" feature. Enabling the serial
# port early in extlinux gives the most complete output in the system log.
sed -Ei -e "s|^[# ]*(root)=.*|\1=LABEL=/|" \
-e "s|^[# ]*(default_kernel_opts)=.*|\1=\"$KERNEL_OPTS\"|" \
-e "s|^[# ]*(serial_port)=.*|\1=ttyS0|" \
-e "s|^[# ]*(modules)=.*|\1=$KERNEL_MODS|" \
-e "s|^[# ]*(default)=.*|\1=virt|" \
-e "s|^[# ]*(timeout)=.*|\1=1|" \
"$TARGET/etc/update-extlinux.conf"
chroot "$TARGET" /sbin/extlinux --install /boot
chroot "$TARGET" /sbin/update-extlinux --warn-only
}
install_grub_efi() {
case "$ARCH" in
x86_64) grub_target=x86_64-efi ; fwa=x64 ;;
aarch64) grub_target=arm64-efi ; fwa=aa64 ;;
*) die "ARCH=$ARCH is currently unsupported" ;;
esac
# disable nvram so grub doesn't call efibootmgr
chroot "$TARGET" /usr/sbin/grub-install --target="$grub_target" --efi-directory=/boot/efi \
--bootloader-id=alpine --boot-directory=/boot --no-nvram
# fallback mode
install -D "$TARGET/boot/efi/EFI/alpine/grub$fwa.efi" "$TARGET/boot/efi/EFI/boot/boot$fwa.efi"
cat > "$TARGET/etc/default/grub" <<- EOF
GRUB_TIMEOUT=0
GRUB_DISABLE_SUBMENU=y
GRUB_DISABLE_RECOVERY=true
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"
GRUB_CMDLINE_LINUX_DEFAULT="modules=$KERNEL_MODS $KERNEL_OPTS"
EOF
# generate/install new config
chroot "$TARGET" grub-mkconfig -o /boot/grub/grub.cfg
}
setup_fstab() {
cat > "$TARGET/etc/fstab" <<EOF
# <fs> <mountpoint> <type> <opts> <dump/pass>
LABEL=/ / ext4 defaults,noatime 1 1
EOF
# if we're using grub-efi bootloader, add extra line for EFI partition
if [ "$BOOTLOADER" = 'grub-efi' ]; then
echo "LABEL=EFI /boot/efi vfat defaults,noatime,uid=0,gid=0,umask=077 0 0" >> "$TARGET/etc/fstab"
fi
}
setup_networking() {
cat > "$TARGET/etc/network/interfaces" <<EOF
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp
EOF
}
enable_services() {
for lvl_svcs in $SVCS; do
rc_add $(echo "$lvl_svcs" | tr '=,' ' ')
done
}
create_alpine_user() {
# Allow members of the wheel group to sudo without a password. By default
# this will only be the alpine user. This allows us to ship an AMI that is
# accessible via SSH using the user's configured SSH keys (thanks to
# tiny-ec2-bootstrap) but does not allow remote root access which is the
# best-practice.
sed -i '/%wheel .* NOPASSWD: .*/s/^# //' "$TARGET/etc/sudoers"
# There is no real standard ec2 username across AMIs, Amazon uses ec2-user
# for their Amazon Linux AMIs but Ubuntu uses ubuntu, Fedora uses fedora,
# etc... (see: https://alestic.com/2014/01/ec2-ssh-username/). So our user
# and group, by default, are alpine because this is Alpine Linux.
user="${EC2_USER:-alpine}"
chroot "$TARGET" /usr/sbin/addgroup "$user"
chroot "$TARGET" /usr/sbin/adduser -h "/home/$user" -s /bin/sh -G "$user" -D "$user"
chroot "$TARGET" /usr/sbin/addgroup "$user" wheel
chroot "$TARGET" /usr/bin/passwd -u "$user"
# Let tiny-ec2-bootstrap know what the EC2 user of the AMI is
cat > "$TARGET/etc/conf.d/tiny-ec2-bootstrap" <<EOF
EC2_USER="$user"
EOF
}
configure_ntp() {
# EC2 provides an instance-local NTP service syncronized with GPS and
# atomic clocks in-region. Prefer this over external NTP hosts when running
# in EC2.
#
# See: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/set-time.html
sed -e 's/^pool /server /' \
-e 's/pool.ntp.org/169.254.169.123/g' \
-i "$TARGET/etc/chrony/chrony.conf"
}
setup_script() {
if [ -f /tmp/setup-ami.d/setup_script ]; then
einfo "Executing additional setup script"
(
cd /tmp/setup-ami.d
chmod u+x ./setup_script
TARGET="$TARGET" ./setup_script
)
else
einfo "No additional setup script"
fi
}
cleanup() {
# Sweep cruft out of the image that doesn't need to ship or will be
# re-generated when the image boots
rm -f \
"$TARGET/var/cache/apk/"* \
"$TARGET/etc/resolv.conf" \
"$TARGET/root/.ash_history" \
"$TARGET/etc/"*-
[ "$BOOTLOADER" = 'grub-efi' ] && umount "$TARGET/boot/efi"
umount \
"$TARGET/dev" \
"$TARGET/proc" \
"$TARGET/sys"
umount "$TARGET"
}
main() {
validate_block_device
[ -d "$TARGET" ] || mkdir "$TARGET"
einfo "Fetching static APK tools"
apk="$(fetch_apk_tools)"
einfo "Creating root filesystem"
make_filesystem
einfo "Configuring Alpine repositories"
setup_repositories
einfo "Fetching Alpine signing keys"
fetch_keys
einfo "Installing base system"
install_base
setup_chroot
einfo "Installing core packages"
install_core_packages
einfo "Configuring and enabling boot loader"
create_initfs
install_bootloader
einfo "Configuring system"
setup_mdev
setup_fstab
setup_networking
enable_services
create_alpine_user
configure_ntp
setup_script
einfo "All done, cleaning up"
cleanup
}
main "$@"
|