TEP-0020: Add s390x architecture support

This TEP proposes the way to add s390x architectures support in Tekton.

Signed-off-by: Yulia Gaponenko <yulia.gaponenko1@de.ibm.com>

teps/0020-s390x-support.md

@@ -0,0 +1,134 @@
+---
+title: s390x-support
+authors:
+  - "@barthy1"
+creation-date: 2020-09-21
+last-updated: 2020-09-21
+status: proposed
+---
+
+# TEP-0020: s390x architecture support
+
+<!-- toc -->
+- [Summary](#summary)
+- [Motivation](#motivation)
+  - [Goals](#goals)
+  - [Non-Goals](#non-goals)
+- [Proposal](#proposal)
+  - [Design Details](#design-details)
+    - [Diagram for pipeline build and test with s390x hardware](#diagram-for-pipeline-build-and-test-with-s390x-hardware)
+- [Risks and Mitigations](#risks-and-mitigations)
+- [Test Plan](#test-plan)
+- [References](#references)
+<!-- /toc -->
+
+## Summary
+
+This TEP proposes extension of the dogfooding part of CI/CD system to be able to
+test, build and release Tekton parts (pipeline, triggers, operator, dashboard,
+cli) for `s390x` hardware architecture. It is based on the idea to support
+non-amd64 architectures, proposed in [TEP 19](https://github.com/tektoncd/community/pull/211).
+
+## Motivation
+
+s390x is a processor architecture for IBM Z and LinuxOne, s390x builds are
+available for many open source products and solutions. Tekton is a great
+framework to build, test, and deploy the solutions, but to be able to do that for
+s390x, it is necessary to have s390x release of Tekton itself.
+
+### Goals
+
+- Describe setup to get access to s390x native hardware.
+- Describe flow to build and test Tekton artifacts for s390x architecture
+(based on "other architectures support" [TEP 19](https://github.com/tektoncd/community/pull/211)).
+
+### Non-Goals
+
+- Specific hardware requirements and k8s cluster maintaining are not covered 
+by this TEP.
+- Missing container images(available for amd64 only) to run e2e s390x tests are
+not covered by this TEP and will be fixed separately.
+
+## Proposal
+
+Extend current Tekton CI/CD system to run Tekton tests and builds for s390x
+architecture. As a result Tekton artifacts (container images and yaml files)
+will be tested and released for s390x in the same way as it is done for amd64.
+
+The details of other architecture setup proposal are described in TEP 19.
+
+Main points, applied to s390x architecture support proposal:
+
+amd64 Tekton cluster will take responsibilities:
+- to initiate all actions.
+- to show results/logs in the UI.
+- to keep all secrets and interact with storages, registries, external systems,
+ etc.
+- to interact with google cloud (google sdk is available only for amd64).
+
+s390x cluster will:
+- operate on native s390x hardware.
+- build s390x container images.
+- run the tests.
+All steps are packed as Tekton tasks.
+
+### Design details
+
+The Tekton code itself is buildable for s390x. The main part of proposed updates
+are required to get access to s390x hardware to run arch specific tasks. s390x
+hardware is provided by IBM and not publicly available at the moment. Also
+there is no cloud provider at this moment to get k8s s390x cluster. To run s390x
+specific Tekton tasks, IBM will provide Z(s390x) hardware(large baremetal server)
+in a yellow zone, which means restricted access, limited ports open, etc. The
+connection between dogfooding amd64 community cluster and s390x hardware will be
+set up via [sshd-bastion](https://github.com/openshift/release/tree/master/core-services/sshd-bastion).
+The idea here is to have a bastion host, running on amd64 cluster and script on
+s390x side to connect to this service via SSH and set up a tunnel so that
+others connections between clusters can be transparently proxied. After tunnel
+is done, all the interaction between amd64 main cluster and s390x hardware will
+be done inside the tunnel.
+Practically it means that special k8s service(s) should be installed and
+configured on the amd64 cluster side, example for tunnel between OCP and
+Z hardware is available [here](https://github.com/openshift/release/blob/master/core-services/sshd-bastion/z/deployment.yaml#L5-L121)
+(OCP is just example and the same setup is doable with vanilla k8s cluster).
+From the s390x hardware side, a special [script](https://github.com/multi-arch/ocp-remote-ci/blob/master/libvirt/tunnel/tunnel.sh)
+should be running.
+As soon as both pieces are connected to each other, the dogfooding(k8s + Tekton)
+cluster can interact with Z hardware using ports, specified in the sshd-bastion
+and tunnel script. Ports are configurable and usually they are 22 (ssh),
+6443 (k8s), 443(https).
+
+Because there is no k8s s390x provider available now, it is required to do k8s
+cluster installation on provided s390x hardware. It can be done via [kubespray](https://github.com/kubernetes-sigs/kubespray)
+and not part of this TEP.
+
+With s390x hardware can be provided:
+- several k8s s390x preinstalled cluster or
+- Tekton task to install new k8s s390x cluster via ssh tunneling connection to
+s390x hardware.
+
+#### Diagram for pipeline build and test with s390x hardware
+
+Sequence diagram for tekton pipeline repo with:
+- k8s Z cluster installation -> new pipeline build -> build installation -> build e2e test -> clean up
+![TEP 20 Sequence Diagram](images//0020-diagram.png)
+
+### Risks and Mitigations
+
+1. s390x specific errors can exist if Tekton code works with low-level memory
+allocation in a little-endian scheme, as s390x is the only architecture left
+with big-endian memory allocation. However at this moment such problems are not
+identified for Tekton.
+2. Usually developers test the new code locally only for amd64, so failing tests
+for s390x with new code are initially expected.
+
+## Test Plan
+
+Existing unit and e2e tests will be executed on s390x architecture.
+
+## References
+
+- PR for [non-amd64 architectures support in Tekton](https://github.com/tektoncd/community/pull/211)
+- Issue [tektoncd/plumbing#495](https://github.com/tektoncd/plumbing/issues/495)
+- Issue [tektoncd/pipeline#856](https://github.com/tektoncd/pipeline/issues/856)
+- Issue [tektoncd/pipeline#3064](https://github.com/tektoncd/pipeline/issues/3064)