[PATCH 1/1] improve apt fetching from rate-limited snapshot mirrors

["'Felix Moessbauer' via isar-users" <isar-users@googlegroups.com>]

The snapshot mirrors apply strict rate limiting, making it impossible to
use them with a default apt configuration. On the other hand, apt does
not obey the retry-after http response header, but uses a exponential
backoff mechanism (retry after 1,2,4,...) seconds. By that, the
currently used 3 retries are basically useless as apt aborts way before
the rate-limit expires.

We change that to retry at most 10 times with a futher upper limit of 10
minutes (both only when using ISAR_USE_APT_SNAPSHOT). This is a
compromise between not stalling failed builds but also making them more
reliable.

Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
---
 doc/user_manual.md          | 4 +++-
 meta/classes/rootfs.bbclass | 5 ++++-
 meta/conf/bitbake.conf      | 2 ++
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/doc/user_manual.md b/doc/user_manual.md
index 284847c8..4b07f903 100644
--- a/doc/user_manual.md
+++ b/doc/user_manual.md
@@ -433,7 +433,9 @@ Some other variables include:
  - `HOST_DISTRO_BOOTSTRAP_KEYS` - Analogously to DISTRO_BOOTSTRAP_KEYS: List of gpg key URIs used to verify apt bootstrap repo for the host.
  - `DISTRO_APT_PREMIRRORS` - The preferred mirror (append it to the default URI in the format `ftp.debian.org my.preferred.mirror`. This variable is optional. PREMIRRORS will be used only for the build. The final images will have the sources list as mentioned in DISTRO_APT_SOURCES.
  - `ISAR_USE_APT_SNAPSHOT` - Use a frozen apt snapshot instead of the live mirror. Optional.
-   `ISAR_APT_DL_LIMIT` - Rate limit the apt fetching to n kB / s. Optional.
+ - `ISAR_APT_DL_LIMIT` - Rate limit the apt fetching to n kB / s. Optional.
+ - `ISAR_APT_RETRIES` - Number of apt fetching retries before giving up. Optional
+ - `ISAR_APT_DELAY_MAX` - Maximum time in seconds apt performs retries. Optional
  - `DISTRO_APT_SNAPSHOT_PREMIRROR` - Similar to `DISTRO_APT_PREMIRRORS` but for a snapshot, pre-defined for supported distros.
  - `ISAR_APT_SNAPSHOT_TIMESTAMP` - Unix timestamp of the apt snapshot. Automatically derived from `SOURCE_DATE_EPOCH` if not overwritten. (Consider `ISAR_APT_SNAPSHOT_DATE` for a more user friendly format)
  - `ISAR_APT_SNAPSHOT_DATE` - Timestamp in upstream format (e.g. `20240702T082400Z`) of the apt snapshot. Overrides `ISAR_APT_SNAPSHOT_TIMESTAMP` if set. Otherwise, will be automatically derived from `ISAR_APT_SNAPSHOT_TIMESTAMP`
diff --git a/meta/classes/rootfs.bbclass b/meta/classes/rootfs.bbclass
index c7011508..03e80018 100644
--- a/meta/classes/rootfs.bbclass
+++ b/meta/classes/rootfs.bbclass
@@ -148,7 +148,10 @@ rootfs_configure_apt() {
 
     mkdir -p '${ROOTFSDIR}/etc/apt/apt.conf.d'
     {
-        echo 'Acquire::Retries "3";'
+        echo 'Acquire::Retries "${ISAR_APT_RETRIES}";'
+        if [ -n "${ISAR_APT_DELAY_MAX}" ]; then
+            echo 'Acquire::Retries::Delay::Maximum "${ISAR_APT_DELAY_MAX}";'
+        fi
         if [ -n "${ISAR_APT_DL_LIMIT}" ]; then
             echo 'Acquire::http::Dl-Limit "${ISAR_APT_DL_LIMIT}";'
             echo 'Acquire::https::Dl-Limit "${ISAR_APT_DL_LIMIT}";'
diff --git a/meta/conf/bitbake.conf b/meta/conf/bitbake.conf
index 13966a62..5fe50787 100644
--- a/meta/conf/bitbake.conf
+++ b/meta/conf/bitbake.conf
@@ -148,6 +148,8 @@ export SOURCE_DATE_EPOCH ?= "${@get_source_date_epoch_value(d)}"
 SOURCE_DATE_EPOCH_FALLBACK ??= "1709565251"
 # Debian snapshots
 ISAR_USE_APT_SNAPSHOT ??= "0"
+ISAR_APT_RETRIES ??= "${@'10' if bb.utils.to_boolean(d.getVar('ISAR_USE_APT_SNAPSHOT')) else '3'}"
+ISAR_APT_DELAY_MAX ??= "${@'600' if bb.utils.to_boolean(d.getVar('ISAR_USE_APT_SNAPSHOT')) else ''}"
 ISAR_APT_SNAPSHOT_TIMESTAMP ??= "${SOURCE_DATE_EPOCH}"
 
 # Default parallelism and resource usage for xz
-- 
2.39.5

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