###Tesing Failover
There are multiple layers. When using a shield:
- MISS, MISS: nothing at the edge and the shield also misses
- MISS, HIT: nothing at the edge but the shield serves state content. Interesting... shield will not serve stale content as a HIT
... presumably a cache will pick up stale content from the shield too?
Will our if(stale.exists) clauses execute on the edge or the shield? Both if we enter vcl_fetch.
- fetch will at some point run on the shield
- 503's from the
origin:- shield should be fne serving stale content here
- but if the edge is seeing a lot of 503's from the shield node will it drop connecting to it?
#Testing orthagonals
- Origin is up or down
- Shield has stale data for the origin within stale_on_error
- Shield has stale data for the origin within stale_while_revalidate
- Edge has stale data for the origin within stale_on_error
- Edge has stale data for the origin within stale_while_revalidate
- Edge considers shield as a downed backend
- Shield considers origin as a downed backend
#Test 1:
- flush edge and shield
- Set origin to up
- warm cache (1 hit while using shield should suffice)
- Set origin to down
- immediately: check we get a hit:
- Expected stale while revalidate serves content
- Then requests from shield:
- Shield enters vcl_fetch and then serves stale (from stale-while-revalidate or from stale-on-error?)
- Edge stores stale content as revalidated
- After stale-while-revalidate time expires: check we get a hit
- Edge gets request which will MISS at the edge and proceed to the shield
- shield contacts origin which fails
- shield serves stale-on-error
- edge stores and serves (stale-while-revalidate timer reset?)
- Warm cache - which with shield should mean one request
- Use a unique request from one edge node only
- Take down origin
- Test we get results both immediately but also after the stale-while-revalidate time has expired
- Also test from multiple edge nodes