build(base-image): make apt install resilient to transient mirror failures

[subrata71]

Description

TL;DR: Make the base-image apt install resilient to transient Ubuntu-mirror connection failures, so a momentary network blip on the build host doesn't red the whole Docker Base Image build.

Background / root cause

The Docker Base Image workflow (deploy/docker/base.dockerfile) intermittently fails at the apt dependency-install layer when the builder briefly can't reach the Ubuntu mirrors. Most recent example: appsmith-ee run 34570186320 failed twice with connect (101: Network is unreachable) (IPv6) and connection timed out (IPv4) to archive.ubuntu.com / security.ubuntu.com. The same base-image build has flaked on apt before (a same-SHA run failed, then passed, on 2026-09-05).

Verified cause: ubuntu:24.04 ships no apt retry configuration — apt-config dump shows no Acquire::Retries and there is no drop-in in /etc/apt/apt.conf.d/, so the compiled default of 0 retries applies. A single dropped connection fails the build. The two GPG-key curl fetches also had no retry, and the PostgreSQL one lacked --fail (so an HTTP error body could be piped into apt-key).

Changes (deploy/docker/base.dockerfile, apt layer only)

• Add a build-scoped apt drop-in before the apt operations: Acquire::Retries "3" + Acquire::http(s)::Timeout "30". It is deleted in the same layer's cleanup (rm -rf), so the shipped image's apt behavior is unchanged.
• Add --retry 3 --retry-connrefused --connect-timeout 15 --retry-max-time 60 to the MongoDB and PostgreSQL key-fetch curls; add --fail to the PostgreSQL one.
• Deliberately not done: no Acquire::ForceIPv4 (IPv4 also timed out in the incident, so it wouldn't help), and no change to the deprecated apt-key usage (out of scope).

This matches the retry pattern already used in this file (the Keycloak jar overlay uses curl --fail --retry 3 --connect-timeout 15).

Scope / honest limitation

This reduces flake frequency for transient mirror blips. It will not rescue a sustained multi-minute total egress outage — retries only help if egress recovers within the retry window. That class of failure is infra, not the Dockerfile.

Verification

• ubuntu:24.04 default confirmed: no Acquire::Retries, no apt.conf.d retry drop-in → default 0.
• Built the exact RUN structure (comment + \-continuation + printf drop-in + cleanup) with docker build: apt-config dump reports Acquire::Retries "3"; the drop-in is removed by cleanup (test ! -f passes); build prints success. BuildKit strips the inline # comment lines before the shell runs (same idiom already in this file).
• All new curl flags accepted by ubuntu:24.04's curl (connect failure exit 7 with 3 retries observed; no unknown-option error).

Impact on existing instances

None. The drop-in is created and deleted within the same build layer, so the produced image is byte-equivalent in apt configuration to before. Fresh install, upgrade-from-default, upgrade-from-customized, and rollback are all unaffected (this only changes how the base image is built, not its contents).

Reviewers / second opinion

Approach independently reviewed by GPT-5.6 sol and reconciled: retries tuned to 3 (not 5), Acquire::Retries::Delay dropped as redundant, drop-in build-scoped rather than persisted, --fail not duplicated on the mongo curl (already has -f), curl retries bounded, IPv4 not forced.

Linear: https://linear.app/appsmith/issue/APP-15960

Automation

/ok-to-test tags="@tag.All"

Note: this is a build/base-image change; the meaningful CI gate is the Docker Base Image build itself. Full Cypress requires a base-image rebuild + deploy preview.

Communication

Should the DevRel and Marketing teams inform users about this change?

• Yes
• No

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